Have Heavy Period Since Childhood. Why Do I Have Back Pain, Dizziness And Sore Breasts?

I have ALWAYS since I was 11, now I m 29, have had extremely heavy periods, but last month I had brown spotting during the time that I was supposed to get my period and it only lasted a few days. I thought that I was pregnant because this has never happened before. I took a couple hpt and they were negative and a blood test which was negative. I haven t gone back to do the second blood test yet because thought it was just too early to show up. Now this month my period was 3 days late which it is never late, the third day I had no bleeding then my husband and I had sex and I experienced some light bleeding. Today, it seems a little heavier like my regular period. All month I have had the symptoms of pregnancy, nausea , extremely tired, breasts are tender and sore, low back pain , dizziness , hot flashes. Is there a chance I could still be pregnant. I really got my hopes up, if not what could cause the brown spotting instead of my period?