Hello I Am 18 Years Old. I Had My Last

Hello I am 18 years old. I had my last period on 06/27/15. The morning of that day I had protected sex and my period started soon afterwards. For the rest of the month I have been stressed. Then again on 7/23/15 I had protected sex again. There were no breakages in the condom, nor cum. Two days before my period began to start I started to have spotting. Something I haven't had until this time. I have not gotten my period yet and it's been 4 days. I did a urine pregnancy test (7/30/15) and it was negative. Since the day my period was supposed to start, I have minor cramps, massive headaches, back pains, and some white discharge, My periods typically come around after 32 days, but over the past few months sometimes they are delayed by 2 days. I am very worried because although my periods are irregular, I have never spotted before nor been this late. Is there any chance of pregnancy. I have been really stressed by this and many other things recently. Please help me.