I Am 46 And Taking Cialis And Prozac For My

I am 46 and taking Cialis and Prozac for my nerves and some time when I'm having sex my penis will get a little soft even on the Cialis. I was on top of the girl and after about 10 minutes it got a little soft and my heart was pounding through my chest and then after 10 minutes I had her to get on top and I didn't have no problem. can you please tell me what's going on