Period... I think?

So the last time I has my period was in July. Right after I had my period was when I started going to the gym. (I’m a big girl and yes it was my first time ever at a gym) all through out the rest of July and August I would push myself at the gym. And once or twice had unprotected sex. Well I completely skipped August of not having a period. And now I think I’ve finally started my period cause I’m bleeding but not heavily but I have cramps and and had sore breasts. Is this my period?? And truthfully I’ve began to think that I’m infertile due to my weight and other health reasoning because every time I’ve had sex for almost a year it was unprotected, he would finish on my top of my vagina and at times it would be when I’m ovulating and every month I would get my period