At three weeks pregnant, you may have an inkling that you're expecting or absolutely no idea. You may even be experiencing some early pregnancy symptoms. Even if you haven't had that Big Fat Positive (BFP) yet, if you've been trying to conceive (TTC), here's what could be going on inside you, right now.

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What's happening at three weeks?

Here are the key things you can expect from your pregnancy at this super-early stage:

• Your fertilised egg travels to your womb (uterus).
• Early pregnancy symptoms are possible (see below).
• An early pregnancy test may give a reliable result.
• Time to work out your due date.

How big is your baby?

Although you may have no idea you're pregnant yet, if you've been trying and have been successful, then right now, your baby is a ball of cells called a blastocyst. It's a teeny, tiny fertilised egg the size of a grain of sherbet.

Conception (where sperm fertilised your egg) probably only happened a matter of days ago, and now this egg is making its way from the fallopian tube to your uterus (womb).

Over the next week it will arrive there, ready to attach itself to your womb and grow into your very own baby, due to be born in approximately nine months time!

What's going on with your body?

In terms of pregnancy symptoms, it's quite unusual to feel anything this early – although not impossible.

Early pregnancy symptoms can include:

• PMS (indigestion, sore boobs, bloating)
• nausea
• implantation bleeding
• discharge
• tiredness

Some mums-to-be say they just 'felt pregnant', even this early on.

Read more about early pregnancy symptoms here.

Don't panic if you don't have any pregnancy symptoms though. The majority of mums-to-be will have little (if any) idea that they're pregnant for another week or two. That's because it's still quite early to do a pregnancy test.

Most tests recommend that you wait until your period due date for an accurate result, which is probably still almost a week away, depending on your cycle.

That's because you need to have enough pregnancy hormones in your system for a home pregnancy test to detect. This usually happens towards or around week four.

However, some modern pregnancy tests are more sensitive, and claim to be able to detect a pregnancy from as early as four or five days before your period is due.

If you get a negative test result but are sure you're pregnant, you could be right. Leave it another few days and try another one. Or try an early pregnancy test, which can sometimes detect the pregnancy hormone as early as six days before your period is due.

Find out when to do your pregnancy test here.

This is the perfect time to start really taking care of your health. Eating well, moderate exercise , and stopping smoking and drinking can all set you up for a healthier pregnancy. And don't forget your folic acid tablets! They're essential to protect your growing baby's health.

What to do: work out your due date

As soon as you find out you're pregnant, you'll want to work out your due date. Using our due date calculator below can help with this.

You'll need to know the first day of your last menstrual period and the average length of your menstrual cycle.

This will give you a rough idea of when your baby is due, but remember:

• you'll get a more precise due date at your 12 week dating scan
• only 5% of babies arrive on their actual due date

A note on weeks of pregnancy

You might be wondering how you can be three weeks pregnant, if conception only happened a week ago. This is because healthcare professionals date your pregnancy from the first day of your last monthly period, not from the day you actually conceive.

So although healthcare professionals say you're three weeks pregnant at this stage, you're actually only one week pregnant. The same goes throughout your pregnancy. So, for example, when healthcare professionals say you're eight weeks pregnant, you're technically only six weeks pregnant. Confusing, no?!

The reason for this is that it can be hard to tell exactly when pregnancy started. Most women conceive around the time of ovulation, but exactly when this happens can vary from woman to woman. Rather than guess at exactly when it happened, it's easiest to just count from the start of your cycle, which is the first day of your period.

It's also not exactly true to say that pregnancy lasts for nine months. Counting from the first day of your last period, your due date will be 40 weeks away. That's actually a little over nine months.

Basically, your due date is roughly the date of your last period, plus 40 weeks!

Luckily, our due date calculator below makes it easy for you...

Things to think about this week: maternity benefits

If you're TTC or already know you're in the early stages of pregnancy, you might want to think ahead to what maternity benefits, entitlements and pay you'll be entitled to once you're on maternity leave.

Depending on your employment status you might be able to get:

• Statutory Maternity Pay (SMP)
• Maternity Allowance
• Shared Parental Pay
• Working Tax Credit
• Universal Credit

Find out more about maternity benefits, how they work and what you're entitled to here.

Your 3 week to-do list

1 Take a pregnancy test or buy one if you haven't already.

2 Take daily folic acid – 400 micrograms should be taken when trying to conceive and for the first 12 weeks of pregnancy. It's important for the health of your baby and will help to protect against birth defects, such as spina bifida.

3 Work out a rough due date .

4 Look into maternity benefits and allowances for maternity leave.

5 Start taking extra care of your health; eat well, and stop smoking and drinking alcohol as soon as possible.

Get more guidance about what's safe to do during pregnancy here .

What to watch this week...

Get expert tips on what to expect at 3 weeks pregnant from our midwife.

What happens next week...

Want to know what happens when you're four weeks pregnant ? Or maybe you've already forgotten what you read last week ? Click on the numbers above to find out more about what to expect at each week of pregnancy.