I'm 20, my girlfriend and I have sex two or three times a week. I have a problem staying hard during sex. I can get hard during forplay. And we'll have sex. But if we change positions I'll lose my hard on. I'm extremely horny. And enjoy it. Just confused why that happens. Any ideas? Also, How can I last longer? I always last about 10 minutes. Which is good enough to make her orgasm, but I'd like to last 30-45 minutes minimum. Any help?