Could i be pregnant...neg tests...or just stress?

had baby 12/07/07....fed and am still feeding just less often. last period was beginning of sept. 2 weeks after period dad was diagnosed with terminal cancer...i lost a good 10-15 lbs in a matter of weeks due to stress...i also stopped taking birth control pill (was only taking it for 2 months) after it made me severly sick.....was late for period by 8 days ...had unprotected but he pulled out before he came (we all know pre has sperm tho which is why im wondering). I have taken 4 pregnancy tests...all negative...no symtoms...was sick this weekend but so was everyone in my family so im guessing it was just a virus. still 3 months with no period tho...with my daughter i knew by 4 weeks. do you think im pregnant?