Firstly, you should get help to arrest this heavy bleeding. Else, it would cause severe anemia
with its added complications. Please see a specialist immediately and get styptics and if necessary, hormones to arrest this bleeding. Subsequently, you should get a proper examination and sonogram to look for the cause of the heavy periods
. You may also need hormone assays. It is normal to have a fluctuation of 3-5 days in each cycle. Ovulation occurs two weeks prior to the onset of the next period. Thus a fertile period spans the week of ovulation. You can plan accordingly. Hope this helps.