My female cat has l discharge?

She is 3 now, i got her spayed about 2 years ago, and ever since then she has had a watery brownish discharge, it seems to bug her about twice a month and she scoots her on the floor. Has any one had this happen, i know it seems like im a bad owner but i asked a vet and they said it should be nothing because she has all of her female parts out, but im starting to think that their is something wrong, im just wondering if anyone has gone threw this with their female cat? and also what could it be? my other female cat doesnt have it. I am on vacation right now and when i get back home i am going to go to the vet and have them check her out, but since ive been away from her ive been thinking about her discharge and im hoping and praying that there is nothing wrong, thanks for you answeres god bless.