Period 8 days late, on and off the pill?!?

So I've been on the pill for 2 months but not consistently ( I know it's terrible and I think I screwed up my hormones) but I was supposed to have a period oct 9 and it never came! The days before oct 7 & 8 I had unprotected sex and they came in me :( so now I'm worried but I've been feeling really sick like cramping and nausea and my breast have been sore but I'm thinking it's because of the pill... I'm not sure what to do, I took a pregnancy test when I was 3 days late and it was negative ... but still no period and I'm worried about stds :( what should I do ??