Ask your doctor to do a full blood count as sometimes having a low iron level (don't take supplements unless you are advised to because too much iron can be bad for you) can cause very heavy periods. You can supplement your diet naturally with foods like red meat, chicken, salmon, certain nuts, raisans etc (do a search on the net for iron rich natural foods) remembering to include vitamin C (via fruit, veg, juice etc) which helps the body adsorb iron better. And I don't think it's due to your weight as my eldest is only 50 kg and she had the same problem until her blood tests showed she had low iron levels.
I dont think it has to do with being overweight, when i was younger i was very thin and i always had really heavy periods too. LIke changing a pad every hour or 2. Now ive had a baby almost a yr ago and cant seem to lose weight but my periods are not that heavy as they use to be. Try getting on b.c. to regulate if your not already on it