This could be an STD or an infection not considered to be sexually transmitted. If it is a non-STD infection, to prevent this in future, you and your partner need to shower and have freshly washed hands before intimacy. Some guys don't realize the importance of cleanliness. Also, different people carry different flora around with them, and some guys will cause more problems for you than others. So I think that means showering and hand washing is even more critical.
You have an infection that you have been ignoring. You may be getting pelvic inflammatory disease. You need antibiotics. See your gynecologist immediately.
Go see your doctor for smears and an STD check up.