What Causes Diarrhea During Period Which Are Heavier Than Before?

hi doctor, i am having diarrhoea,(frequency 6-7 times a day through out my periods), and a feeling of uneasiness, and tiredness since the last couple of months and my menses have become way much heavier than before (since the last couple of months),
why is it happening when it did not happen before and what do i do for now or in the long run as it is restricting me from functioning like normal like i used to? Kindly advise.
(i am 24 yrs old/55 KG/5Ft 6IN/ my periods statrted when i was 12 yrs old, i do not take any pills or medication other than Iron Tablets - Ferrous Fumarate has no side effects on me. I have an outdoor job and can't take a few days off or stay at home).
Thanks