I recently bought my first home, a 60 year old place with one bathroom. We have a gas water heater in the cellar, and it goes up to the first floor to the kitchen, washing machine, and bathroom.
Now the problem. Not all the surprising, we have to wait for hot water to get to any of the faucets. However, once the hot water arrives, the water pressure drops dramatically. This phenomenon can be witnessed at every sink, the shower/tub, and the washing machine. Also not surprising, we can't run more than one thing at a time, or the water pressure drops dramatically for hot and cold water. It makes taking a shower fun when someone flushes the toilet! :)
When you run the hot water in the tub (two handles), you turn it on, and as expected the water pressure builds as you turn the knob. You wait for the water to get hot, and you know it is when you hear *THUNK*. After the loud "THUNK", the water pressure drops down to nearly nothing, then you turn the knob more and more, and all of a sudden, it's coming out full blast. If you want hot water in the shower, there is no in-between, full blast or nothing. The cold water knob does not do this, and other than the hot water slowing to a trickle at ever other faucet, they don't do it either (except for the bathroom sink, it whines a very high pitched noise when the hot water gets to it).

The bathroom is all newer plumbing, it was put in within the last 10 years. It used to be a bedroom, so the piping to the bathroom is all new-ish.

Any ideas would be greatly helpful! I'm hoping not to have to call a plumber on this, making my mortgage payments are enough fun!

Sounds like a classic case of debris in the hot water line. Start with draining water out the bottom of the hot water heater until it runs clear. Repeat monthly. If that doesn't help, work you way upstream breaking the pipes wherever you can and run some hot water out. Somewhere there is junk in the line that is carried to where it blocks the pipe about when hot water get to the faucet.

If Tom has another idea, try it first.

As usual, Labman hit it right on the button. Your 60 year old house has galvanized pipes the same as my 50 year old one. These pipes build up mineral deposits,( iron oxide) over the years that can drastically cut back on both volume and pressure. While the piping in your bathroom may be "newish" the mains the feed it are not. It might be time to
Bite the bullet and consider repiping the rest of the house Good luck, Tom

Thanks so much. I'll have to see if I can't figure out how to drain the hot water heater in the cellar. Hopefully that will help some.

I don't know of how to get to any of the plumbing other than that. I think it's under the house and my claustrophobic, arachnophobic self would most likely freeze up before I got under there.

I had no idea that stuff in the pipes could cause the problem of the hot water handle to turn and turn and turn with no water until suddenly it's on full blast. Maybe I'll have to figure out how to take the handle off and see if something is in those pipes. Right after I figure out how to turn off the water to the bathroom that is!

Thanks so much. I'll have to see if I can't figure out how to drain the hot water heater in the cellar. Hopefully that will help some.

I don't know of how to get to any of the plumbing other than that. I think it's under the house and my claustrophobic, arachnophobic self would most likely freeze up before I got under there.

I had no idea that stuff in the pipes could cause the problem of the hot water handle to turn and turn and turn with no water until suddenly it's on full blast. Maybe I'll have to figure out how to take the handle off and see if something is in those pipes. Right after I figure out how to turn off the water to the bathroom that is!

Each fixture has its own shut offs. Shut the water offf and open up the valve.
Check for crud or rust flakes in the inlet ports of the cartridge. Now, with the valve still open and apart, turn the water back on for a minute to flush out the supply lines.
To flush your water heater out follow these directions.
Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Let me know how you make out. Cheers, Tom