I am 25 years old. Me and my fiancee made love with each other two months back i. E. On 17 feb and two days later I had my periods, which was on time. The next month it occurred on 18 march and 15 on this month. I normally have a cycle of 28 days which last for 4-5 days but since last 2 months, the flow on the first 2 days were as usual heavy. But on 3rd day it was light and ended up. I even tried test kit last month but it was negative. I am concerned why this is happening. Is there anything serious?