I am probably not the best one here at Wetpixel to suggest ways to get out of your dilemma but here goes:
“Break the rules”
restrict yourself to one lens and really work it for all you can get out of it
Intentionally introduce various amounts of blur to your photos
Use “rear flash” if your equipment allows it
Dive somewhere where you normally wouldn't dive (do this safely though)
Try different lens and equipment combinations i.e. wide angle lens with teleconverters, small apertures and long shutter speeds, etc.
Dive without your camera once in while (it's amazing the great photos you will see when you don't have your camera gear with you!)
Try available light underwater photography with and without filters
Vary the position and number of strobes you use when you photograph underwater
Shoot with and without diffusers
Look at the work of other photographers and maintain a file of photographs you admire (best done with magazine photos and try to figure out what you like about them)
Execute images in terms of style from that list of magazine photographs that you admire
Study your results with a non critical eye and decide on what you like about your images and improve or expand on these concepts
Challenge yourself on a concept or theme...
Remember that there are other things besides fish to photograph when underwater such as seascapes, diver interaction, diver portraits, environmental change due to human interaction etc. These issues can be extremely interesting to non-divers due to their lack of familiarity with the issues that we see every time we dive.
Allow yourself to “break the rules” and don't become overly critical of yourself and your results.
You already have enough underwater photography kit to compete effectively with everyone. Shoot the image the way you see it in your mind's eye and the worries about post processing will cease to be a major issue.
While this is not an exhaustive list, this should be enough to get you re-started in the right direction. I know others will have more ideas you should be able to use.
Good Luck, hope you get some great results.