Always too soon...

Every time my SO and I have sex the fore play is amazing but when it comes to the actual act it's very short lived on his part.  I think the longest he's lasted has been maybe 3-4 minutes at this point.  He seems to think it's because of his ADHD. I'm not so sure.  I'm not complaining but it would be nice if he could hold out a little longer. Any ideas or should he see a doctor?  And if so how do you go about that conversation without hurting his pride?