My period was five days late, now I'm having heavy bleeding and pain

I had unprotected sex on the 24th of February a week or so after my period. We used the pull out method. Yet I had gained weight, tender breasts, nausea, and of course fatigue. This is all normal for me when I'm on my period. The day after I was expecting my period I got brown spotting for two days. Then it stopped for two days. Now on my fourth or fifth day of panic I'm bleeding but it's quite heavy and I'm in a whole new world of pain. I've been having steady abdominal pain all week...please help. I was going to wait till next week to take a pregnancy test just to be sure but now this happened I'm just not sure what's going on. Is it possible I was pregnant and now I'm having a miscarriage or was it just late period because I stressed myself out worrying? Please answer quickly I need help. I don't know what to do.