Diarrhoea and long periods

Hello,
I am 43, mother of 3. Recently had bloods taken to show low platelets, low calcium and iron. The last 5 months my periods have started on day 28 (I’ve had no issue with periods apart from a bit scanty when very active)
They then by evening of day 1 are dark brownish stringy. This continues for a few days. Pms and fatigue is very noticeable. Then day 5or 6 period flows very heavy along with diarrhoea cramps. Urgent and copious and often passing maybe 6x. Feel weak and tired and abdomen doesn’t like to have anything tight around it. Immune system Is low and often get a sore throat and cold around this time, white tongue coating. The heavy flow continues for 2 days and then lightens finishing usually on day 10. I eat healthy foods limit sugar and haven’t been able to have diary for the last year anymore as it affects my sinuses and induces hazy headaches. I’m drawn to Sepia so have had in in the last few menses but didn’t help with diarrhoea.
Any advice much appreciated.
Thank you!