There are several ways of finding that out, possibly, even before you go to the doctor.
The first and early sign is frequent urination. The stomach feels bloated (because it is caused by hormonal changes in your body). The nipples feel a wee bit sore and the breasts feel heavy. You are, probably, getting irritated with things that normally do not irritate you. And, you are hungry all the time. Your liking or dislike for certain foods is slowly getting converted into aversion or craving.
One of the first things you may need to do is to get the home pregnancy kit to test yourself.
You need to be careful when you do these tests because they could give you a false result. It could be positive, false positive or even negative, at least, in the early days of pregnancy. The best way to confirm the pregnancy is to get a proper urine test or a blood test which is the most decisive.
A blood test is largely relied upon because it can confirm whether you are pregnant or not, approximately about 10 days after missing your period. Such a test will show the presence of hCG or human chorionic gonadotropin. hCG is produced by the cells of a fertilised egg which slowly increases in the body. It is this hormone which is not easily detectable in a home pregnancy kit particularly in the very early days of pregnancy. A home pregnancy test can detect hCG only when its level is high in your blood. This is one reason why such kits can give false results.