Pregnant or Period?

Hey I was wondering if I could be pregnant or if it's my period. I'm very irregular since I almost never get my period, probably the last period I had was in July. So I had sex with a condom on Saturday, and since yesterday ive been getting these bad cramps, diarrhea and light bleeding from my vagina. I tried looking it up online but it just leads to implantation bleeding. Can this even be possible? It just happened three days after sex so I'm freaking out. Also how can cum even go through the condom? It didn't break so I'm getting paranoid if something went wrong, or if it's just Mother Nature finally letting me my period?