What Causes Heavy Menstrual Bleeding?

Hello Doctor, I am 32 years old. 2 months back, I had taken Primolut N for stopping my periods. The dose was 1 tablet per day and I took it for 4 days (1st Feb to 4th Feb). My first period started 10 days after stopping the tablet, on 14th Feb. The flow was less than usual. My 2nd period was little late (after 6 weeks), on 28th March. The flow was again less than usual. My 3rd period was on time, after 4 weeks and started on 23rd April. However, there is very heavy bleeding this time. I am changing completely soaked up large size pads in every 3 hours since last 2 days and have dumped almost 10-12 pads till now. I have never had this level of heavy bleeding ever in last 20 years. Is this normal or there is anything to worry about? Looking forward to your response. Thanks.