Is it possible to be 21 weeks pregnant and not know? I'm only 19 and the last time I had sex was in may junes period was normal but then July it was a little lighter then August it was way lighter and way shorter. In September I didn't even get one. Being 19 I wanted to not think I was pregnant. My friend and I talked about this and she told me to take a test and when I did it came out positive. But I have had no syptoms except being tired and missing periods.

Yes, it's possible. Make a doctor's appointment immediately to get a blood test and prenatal care.