Well, since I'm in the same boat as you at the moment, I'd venture to say it's elbow tendonitis.
As for the cause, it's most likely the triceps extensions. For me, heavy triceps extensions with a bar (EZ bar) are the culprit. If I do anything for less than eight reps and heavy weight, I am in pain for weeks and weeks.
I've found that doing lying dumbbell triceps extensions helps prevent tendonitis, if, I don't already have it. So, although I stopped the EZ bar lying triceps extensions (aka Skullcrushers or nosebreakers), I'm still doing dumbbell extensions and having some discomfort.
However, it will go away in due time, and I also started using FLAMEOUT a few weeks ago. So I'm hoping that will also begin to kick in and help my elbows.
Ironically, all the pressing exercises have never given me this problem even when I was using Westside.