I had sex on Oct 3rd. and about a week later i started not feeling well, like sick to my stomach and having severe cramp like pains. but i was due for my period for a couple weeks, but I had possibly what you would call as " implantation bleeding", a nother week and half passed with not feeling good, i took a pregnancy test on oct 17th the day before i was due for my period. it was neg. but i still have not gotten my period. Should i do my next tomorrow morning since I am going to be 3 days late or wait?

if you do not start, you should indeed take another test, or call your doctor.

there is plenty of false neg. in hpt.

You would not have symptoms a week after having sex, even if you were pregnant. Implantation bleeding is somewhat rare and "intense" cramping wouldn't happen.

That being said, you could be pregnant, but those symptoms may be a coincidence.

Take a test with first morning urnine. If you're still unsure and your period gets to be 2 weeks late, call your doctor.