I have been masturbating ever since I was 13-14 multiple times a day. I've noticed over the past year my erections have been getting weaker and weaker over time. The only reason I haven't gone to the doctor was because it simply wasn't on my mind when I masturbated. I recently went to the doctor for this and she said she couldn't think of anything it could be. I asked if it could be a hormone imbalance, she said no. Diet, no. She checked me for STDs and came back negative. I'm starting to get worried as my girlfriend and I are getting physical now and I don't want to disappoint her.