3 weeks late but had sex one week before period was due

hi, can someone please help! I'm very confused at the moment. I was due on my period exactly 3 weeks ago but had unprotected sex 5 days before that. However, my period gave it a miss and I've done numerous HPT all negative. i had a miscarriage a few months ago and got a positive at 5 weeks and had symptoms such as sore boobs and nausea. However this time round I don't have sore boobs. I do feel nauseous and had dizzy spells like none before and tummy cramps and discharge. It feels as though I'm going to come on and have thought I had but only to find it was discharge(sorry TMI) a week ago I had lower back pain for two days and I never ever had lower back pain. ive never missed a period only when I was previously pregnant. I'm supposed to be due next week for my period. is it too early to test?