Strange symptoms! Please help!!

I had brown spotting 3 days ago and then started getting heavy bleeding. Had heavy bleeding for 2 days and 1 night and then normal bleeding thereafter. I've also had severe cramps and and very tired and feel dizzy which is very unusual because during my periods I have never had any pain or any problems ever they have always been so easy. Never had unprotected either. What could  be the reason ? Are there any chances of me being pregnant and bleeding during pregnancy ?? I can't predict my cycle as I have always had irregular cycles.