I've noticed that after doing pushups my one elbow hurts a bit.. any ideas?

One word: tendinitis (possibly). Some of your arm muscles are attached right where the elbow is located. You may be straining one or more and this is causing the tendon to pull excessively from the bone. If it is tendinitis, you'll have some swelling and tenderness, best to ice it right away.

Could be a previous injury or strain you've had in the past. Not sure what activities you've done 'growing up' or since, but I know myself, after playing years of baseball, I know if I throw the ball hard now, my elbow acts up. It doesn't bother me in my weight training but it's the idea that a reoccuring agravation of site might be happenning when your doing your pushups.

When you are doing push up keep your elbows as close to your body as possible. When your elbows flare out it puts stress on the joint. Also start taking Glucosamine and chondroitin it does wonders for sore joints.