How normal is this? Sorry it's kinda long

I got my period pretty late, around 15-16 and it's always been really heavy and irregular, but I never really had any cramping or nausea etc.

After I lost my virginity my first period was absolutely horrible, the worst week of my life. After that relationship ended I stayed single for about a year and didn't so much as masturbate. My periods were still heavy and irregular and I had some mild cramps every now and then but basically it was never a bother.

Now. I'm in a relationship again and after having sex the first time my period was so bad I couldn't get out of bed, burned my stomach with heating pads which I've never needed before and literally slept and wanted to cry the whole week. It's gotten better 7 months later but the cramps are still pretty intense.

Why does it seem like being sexually a five makes my periods worse? (But sex itself is never really painful even when I lost my virginity)

Is that normal?

Can that along with the heavy bleeding and irregularities mean I could be infertile??

Just really don't understand sorry it's so long