What Causes Dark Brown Vaginal Discharge With Particles?

i am 41 yrs old female, Recently,I noticed that my vaginal dicharge has brownish small particles ( similar to coffee or pepper) and has strong decaying odor, It left a greying/blackish stain on my panty. I have this before and after my periods. Also, my period has darker color (more like brown) than before. Also, when I have intercourse with my husband,, I felt discomfort. What is happening to me ?