What you are facing is a very common side effect of SSRI's and you can discuss it with your consulting doctor. It's a temporary effect and it wears off eventually. What you can do is change the timing of taking your pills. As in if you plan to have a sexual contact at night take the pill in the morning or so. Increase your water intake as well. Masturbation also doesn't cause any of this problems. All your questions and queries can be answered by your consulting psychiatrist. And after evaluation if he thinks there's a need for prescription he'll tell you about it.