HELP!!!

I had unprotected sex 12/23 and he finished inside of me, but I took a plan b about an hour after. The next day or so there was brown discharge. I’ve gotten what I think was my period on 12/31 and when it went away I spotted for a few days after. However, I took a pregnancy test 3 weeks after the unprotected sex and it came back negative, should I still be concerned? The reason i’m asking is because I have been feeling nauseous, light headed, and my body has just been feeling hot, also lots of trapped gas could that be covid 19 symptoms or pregnancy symptoms?