What Is The Cause Of Heavy Bleeding With Lumps During Periods After 3 Months ?

I am having my periods after 3 months and am bleeding heavily on my 6th day. Its like ab explosure of heavy bleeding wit huge lumps coming out after it. I am having this since 11 last night. Yesterday from 11pm till 4 am it was continuous flow and then it subsided. I tested before a month and wasnt pregnant. Can I know what is the cause and any solution?