Really late for my period

I'm really late for my period but all of the pregnancy tests i've taken come out negative. im not trying for a baby although i have had unprotected sex as i thought i was infertile due to my medical history.

this is the latest my period has ever been and i keep getting small pains where i would usually get cramps. I haven't lost or gained an excessive amount of weight, although i have been on a diet.