21 weeks pregnant

do you believe ,. I don't know that I'm pregnant. I just learned ( the previous day) when I use pt, that was positive. it is so quick to react because I was 21 weeks pregnant! I do not really know because my stomach is already big even if i'm not pregnant , and I have no symptoms so that i just ignored it. and also my period was always irregular (once every 1month to 2months). I don't smoke and drinking alcohol so that i'm pretty sure or i hope that my baby is fine. But now i need to take some check-ups, vitamins and milk to ensure my babies health.