All great answers here 3D.
Your working to hard, to long. First thing I did last year was increase prices. I just went up 4%, it did make a difference. Helped cover for increased costs from suppliers, a little went for the rediculous fuel prices at the time.
However, suppliers did not come down in their prices, they all went up, including FedEx, and stayed there. So the first logicla thing to do is increase a bit. At least 4% across the board. Then go back take a look at what supplies went up the most, or that you may be undercharging for, and increase those again, over the first 4%.
You most likely will stay as busy as ever, but, you'll feel a little better for a while. Till the hours kick you in the head again. That could take a couple of months. Possibly by then, you'll see where the economy "might" be headed, then drop the slow payers first, second, any office you have to ship to, then any office that is the farthest drive, then the office that calls and talks a lot and uses up a lot of your time. I'm sure others here have ideas on who to drop off first.
Mike.