What Causes Periods To Be Heavy And Light Alternatively?

This is Joy from Delhi. and my wife (24 yrs) is having regular periods from last 45 days. some times it's heavy or some time it's little one. I have visited doctor, she has written some test and I have done it and got result i.e TSH (result-5.48 uIU/ml), Blood sugar (result - 92.0 mg.dl), prolactin (result-7.16 ng/ml) and Insulin (result - 13.20 uIU.mL).

Please advice me what is the problem