As for low pressure:
Is the low hot pressure from all faucets in the house or just one... or a few.
First remove the aerators from each faucet and check to see if there's any debris buildup on the screens of them. If so, clean them out and see if that helps.
Another thing that comes to mind is maybe a valve not fully open. If you have a valve on the line out of the water tank be sure it's fully open.
Those are the two things I know to check on that part of it... As for running out of hot:
If it's an old shower head, it may be that it's just allowing too much water to pass... as in 4 or more gallons per minute. That's the problem in 95% of the cases we run into.
Hardware stores will carry a restricter washer for about a dime that you can put on it to try.
You might also check the temperature dial on the tank and be sure that it's at least at the mark that they call standard. I don't know what temp. that is, but typically there will be an arrow or dark line at a point midway between the lowest and highest setting.
I hope something here helps