I’m 21 possibly pregnant with ex boyfriend

I’m 21 my ex and I broke up over a year ago but we never stopped seeing each other. I was up visiting him a couple weeks ago and we used condoms and I was on my period. My period was only like 3.5-4 days so I don’t know if maybe I ovulated earlier than most people. I can see something but I can’t tell if I’m going crazy or not. I’ve been super nauseous the past 4 days and I’ve started to cry randomly throughout the day. I’d only be like 3 weeks so I’m really worried.