Early miscarriage?

I had unprotected sex twice 3 weeks ago and my periods are irregular so I’m not sure when I was supposed to get since I just got it about 3 weeks ago too. 2 days ago I’ve had the worst cramps back pain I’ve ever experienced I’ve been feeling so sick and never like this before and I’ve been bleeding non stop filling up a couple pads a day. Usually my periods are very light can almost go a whole day a night without having to change the pad and never get cramps and I’ve had my period for years so it’s not like I’m new! Could this be a early miscarriage I’m at almost 4 months since unprotected sex, took a pregnancy test at 2 weeks cake up negative but I feel like it was too early