Weird Discharge

Please help: So for years I've been randomly getting this pinkish reddish discharge that kinda smells fruity. I sometimes even have to put a tampon in so I don't stain my panties. I talked to my gynecologist about it a while ago and she said that they had already tested me for any of the STD's that that could be a sign of and they all came back clean. But I have no idea what it is! Has anyone else had this? It lasts for days sometimes!