I had unprotected sex, but may have gotten my period. could i be pregnant?

so about 3 weeks ago, i had sex with my boyfriend and he went inside of me only for a second without a condom at first and then we put a condom on. my period was supposed to come 5 days later but it came two or three days after i had sex. i was very crampy the day after sex and for most of my period. usually, my periods are very much the same when i had them but this one was very light at first for the first 2 days (which isn't normal) and then it was a normal 5 day period. i have to pee often but that was like that before... i just think i cant empty my bladder completely, but i'm not sure if its more often urinating than before. also, when i'm laying in bed on my stomach, i feel this weird feeling in my stomach, like pressure or something beating, its more in my lowerish stomach, but it may just be in my head (but it is unsual) i used to eat alot but now i feel as though i dont eat that much anymore, im not sure if its because im being averted from food because i feel sick or because i just dont think i need to eat it. could i be pregnant? please help, thank you