30 year old with erectile dysfunction...is it in my mind?

I'm a healthy 30 year old male with ED, though I don't know if I would classify it as full on ED (yet). I have trouble gaining a full erection and it usually takes a while before I can get one although every time I have sex, I eventually will get one but it takes a while and when I do it's only semi-hard. I didn't have this issue when I was younger. I would be fully erect and standing tall and proud by the time my girlfriend had her clothes off, but now, I can't even get erect when she's giving me oral sex. It will take 15-20 minutes of foreplay for me to get semi hard and during sex, I'm always thinking about maintaining it.

I have heard alot of things, that I'm thinking too much about it and not focusing on the pleasure but focusing on being hard. I've heard that exessive masturbation causes it and too much drinking can cause it too. I'm very healthy and play hockey 3 times a week, work out and excersise (although my diet isn't very good and I do drink alot).

I'm worried that it will get worse. My doctor presribed me Viagra and it works, but I don't want to be using it for the rest of my life to get an full erection, especially since I'm only 30. It's stressing me out and I'm looking for other advice on how to fix me. I've heard that accupuncture might help since I might have bad blood flow.

If anyone can help and perhaps give some advice on types of food or diet, or habits to cut or anything else that worked to help them please let me know. thank you.