I have always had blood clots while menstrating. My doctor says it is normal. I also have two flows I guess like you. where I start one day with a super heavy flow then it slows the next day then it almost completly stops the third day then it kicks off again on the fourth day full flow and heavy before slowing down and finnally completely stopping on the seventh day. Its weird but I think It is normal and you don't have to worry about it. But I am NOT a doctor so just to be safe you could ask your gyno.