How can I treat my possible Impotence?!

How can I treat my possible Impotence?

When I am by myself, I can achieve erection pretty easily, plus it happens when I dont want it to, like if I happen to rest my arms on my pelvic area. I'm sure you guys know how that goes.
When I'm with my gf, it's a different story. When we arn't tring to do anything, and she is just teasing me, then I can get erected. Also if we play around, but not intrested in having sex, then usually I can get up, but sometimes I can't. The few times we've wanted to have sex, I'll get really nervous out of excitement, and sometimes when we arn't going to have sex, I'll be thinking about it, and can't get up.
Basically, If I get nervous or stressed then I can no longer get up, or if I do it's not full, and quickly goes away.
I've tried to clear my head, and relax, but I still have trouble. The other night, I was just slightly nervous, and I couldn't get anything.
It's really bothering me, and I want to be able to pleasure her.
What can I do?

1 month ago
If it continues, I'll try to seek professonal help, but I'd like to see what I can do about it myself first.

This isn't impotence. It is nerves and fear and not unusual.

Ease up on the expectations.

Also consider learning some oral skills. There is almost no woman that doesn't appreciate that plus you will find that the arousal for you will help you perform as desired.