What Causes Irregular Periods And Fowl Menstrual Blood Odor?

I am 41, have Hypothyroidism and in the last couple of years since having my little boy my periods have been irregular. Either missing month or two or only having a break of two weeks between. But they have been heavy for the first day or two then go very brown and slow to end with a foul smell to them. I haven't been sexually active over 4yrs so i wonder what is causing this. It makes me very conscious as the smell is very strong. Can you offer any advice?