What are you doing in your attempts to improve? What kind of training regimen are you on? Do you incorporate a lot of "specific" training (on a mound, correct distance, at a strike zone/catcher, game intensity,...) or are you doing a lot of drills that may be non-specific?
Another thing to think about is that, the higher you get in terms of velocity (mid-high 80's), the harder every extra mph becomes. It's pretty much an exponential curve. In other words, patience, my friend. This ain't easy. If it were, everyone would be doing it.
I hope you can get some video soon.