What Could Cause Thick Yellow /green Discharge?

Yes. I have been to my primary doctor and an ob gyn and was tested for stds. All came back negative. But I have a thick yellow/green discharge that won t go away. This has been going on since October of last year. They say it s not a bacterial infection or yeast infection. A lot of times I can feel my discharge coming out. Then it irritates my vagina. I ve tried changing soaps and detergent also. I don t know what else to do. Im 44 years old. Could I be going thru menopause?