Intermittent bleeding during due periods

I was sexually active last month. When my periods were due, I started bleeding like normal periods with clots. Blood was bright red in starting but colour slowly changed to little dark red.After 36 hrs of bleeding (which sometimes increased and again decreased and again increased-decreased) it stopped. After 8 hrs of bleeding stopped, it again started slowly which increase heavily with bright red in starting and again little dark red. Again after 7-8 hrs of bleeding, it stopped. After that I did urine pregnancy test which was negative. Again after 8 hrs of bleeding stopped, it started slowly which increased again with bright red colour. There isn't any breast pain or changes. Few hours before last time bleeding started, I started having fever and my whole body is paining. There isn't any frequent urge to pee. I am having little nausea and had vomiting 2 times few hrs ago. 2 months ago I had an Pelvic ultrasound where there was cyst on left ovary. I never had such periods. What is this?