2 weeks late 1 day heavy bleeding then nothing but brown spotting

I know there is always a chance for being pg when you have unprotected sex a few slip ups and a late period but no doctor seems to want to listen and i would like answers or thoughts. have been using the pull out method for about 3 months.  I was over 2 weeks late started some very light brown spotting then over night had to get up 3 times to change tampon and pad was bleeding very heavy with half dollor size blood clots every time i urinate that lasted one day. the next day nothing not even a spotting then today brown spotting again in the mists of all this mess left abdominal cramping, headache, nausea, tierd, lower back pain and very moody. when i had the heavy bleeding i went to the obgyn he did a quick pap and said possible miscarriage but he doesnt think so they sent me for a urine test and it was all blood i dont think i urinated at all (sorry if tmi) tried to tell the doc but didn't say anything except showed me the test result that said - he told me it was just my period i was fine... that was 2 days ago and now i am spotting brown after having nothing yesterday anyone have any advise or opinions please help i am 26 and just trying to figure out if this is normal period behavior or if i need to look deeper into what is going on and if its possible to be pg that would be great to.  Just looking for advise if anyone has any