There are two things that could be happening here.
1- Most likely it's tendonitis
2- What you read in Arnolds book. It's kinda like Shin splints for the arm.
What you need to do is improve your w/o's in terms of how often and how much rest you give yourself, how heavy you go and the exercises you choose to do.
As far as your metabolism, that's got nothing to do with your amount of time in the gym, your gains will be retained from eating not spending more time in the gym.
Myself and a few people here do have similar problems and I believe it can be taken care of through training around it
For now, lay off the weights for 2 weeks and ice your elbows.