If you can finish by masturbastion, but not by having sex with your partner, could it possibly be a lack of sensitivity to your area caused by the medication you're taking? There are so many side effects of medications, some of them aren't even known, and everyone is different and can experience different side effects. I was put on a Parkinson type medication to help control my restless leg syndrome because the others had stopped working. After an increase in the medication and about 1 month, I started having narcolepsy type episodes. I would nod off in the middle of a conversation, or while watching tv. I was afraid to drive for fear of falling asleep at the wheel. My doctor had her technicians, and P.A's researching all my med's trying to figure out which one could cause these side effects. My husband actually figured it out. I stopped taking it, and by the next day, I was fine. Of course, then we finally realized that my iron was so low and I needed an iron infusion, and that's why I was having restless leg syndrome and why the meds didn't work.