What Causes Irregular Bleeding,cramps And Bloating?

Had my period on time, came off after 5days on the Friday like usual, Sunday morning had heavy bleeding again and then finished that afternoon. This has never happened to me before. On Sunday I had nausea, dizziness, stomach cramps, it is now Monday, the bleeding has stopped but still have nausea, heartburn and a bloated stomach? What is up with me?