What Causes Discharge From Bartholin Cyst?

Hi I suffer from bartholin cysts and i ve had it drained 5 times this year. Finally one doctor found a way to keep it open, she made an incision on the side of my labia and not inside my vagina where they normally drain it from and packed it with packing tissue, sewed around it to keep it in for two weeks while it drained and in that process my skin healed around it so once the tissue was removed it left a permanent small hole. Well that worked! my cyst drains on its own, most times i don t know when it will so i have to wear a panty liner all the time..but when it does the fluid smells horrible and i was just wondering why is that?