What Causes Medial Epicondylitis And Cubital Tunnel Syndrome?

I have medial epicondylitis and cubital tunnel syndrome as well as tensynovitis of the left wrist. I sit at a desk all day long and have in the last 6 months worked much overtime, I feel this is all work related. Several years ago I had an injury to my left elbow at work and really never got full recovery was diagnosed with epicondylitis a that time. Is there a way to prove it is work related now that I am having a reacurring problem?