You could have thrush that needs to be treated with an over the counter antifungal. You may want to take a tablet (ie fluconazole) or use a cream or pessary (ie clotrimazole).
What did the doctor say when you saw him the last time.
But at any rate you probably need to see someone and get it diagnosed.
well my advice would be to go see a doctor , because if the doctor gave you something after it and it went away, and its back after having sex, then that means you should go back and he might be able to give you something !