Matt356, you have to describe a little more detailed, what happens:
How do you get hard in the first place?
Has it always been like this, or has the problem started at some point in your life?
Are you 100% hard, when you are hard?
Are there periods or situations, where it is more easy for you to stay hard?
Have you discussed this with you girlfriend?
Are you stressed or going through a rough period?
Do you think it is physical or psychological?
JL
(and as you might notice from the questions, I have been studying psychology)