What Causes Vaginal Discharge Along With Pressure In Pelvis Before Menstruation?

I am 38 years old..my periods are regular...i have noticed in the past 6 months that I have alot of discharge the week before my period...as normal my period came and went but I have not stopped having discharge...i find that now I have to keep a tampon or pad at all times...my discharge was clear or white but is now very thick and has a brown tint or sometime pink tint to it and is very slimy in appearance. .it also has a very foul odor...it have alot of pelvic pressure..as if I have a bad stomach ache all the time..please help