Why Am I Spotting For A Weak Before The Beginning Of Menstrual Cycle?

Hello I had a question involving an unusual menstrual cycle that I've been having for a little while now. Its like for about a week or a little less I will have like spotting but not like real heavy, then after that my menstrual cycle will actually start and it will be heavier and I have all the stomach cramps and what not... so its like I'm noticing blood for two weeks but the first week isnt really my menstrual cycle its just spotting