My Last Period Started On May 15, 12 Days After

My last period started on May 15, 12 days after it ended I started bleeding again some days I’m spotting with barely any blood and other days it’s out of control it’s going on 10 days that this has been happening. I’m having pain in the right side of my pelvic area. I’ve also had an awful migraine for 2 days now and occasionally when I stand I become light headed. I am on birth control and my periods are always on time so I’m not realy understanding what is going on. Any suggestions?