Your history suggestive of irregular and some time periods in 15 days which pointing towards sometime anovulatory cycles.. but your periods are painful when it is normal ovulation.
So, you need hormonal profile to know status. and need usg to rule out if there is any reason or not which can cause both heavy and painful periods...
Next Steps
meet gynae doctor plz
if everything will be all right your doc can advise monthly hormonal medication to regularise your periods..will also help in pain
treatment will be according to cause