Hi, I Had Intercourse During The Time When I Was

Hi,
I had intercourse during the time when i was fertile and about to ovulate. My last period was suppose to be on the 20th , had intercourse around the 30th. 5 days later i started to spot for around 3 days but ive read about implantation bleeding and mine was a bit heavier with clots involved.. the nurse said its just my normal period. now its been past my regular scheduled period and ive always been on time and i've been 4 days late so far. I have taken pregnancy tests but all came out to be negative. if i am pregnant i would be about 2 to 3 weeks pregnant. is it too early to do the urine test. could i still be pregnant. could it be a etopic pregnancy or just stress/late period.