I wanna take a hot shower in my own home!!!

The water coming out of the bathtub faucet is lukewarm at best, unless someone flushes the toilet for me while I'm in there. :D

I can get hot water out of the sink faucet, and I can get hot water in other parts of the house. It's been a gradual change. I noticed it was a little cool a few weeks ago, but chalked it up to other things (running laundry etc.)

The bathtub faucet operates with one knob that turns from hot to cold, and it's been installed at least 10 years. I've never replaced any parts, so I'm hoping that's where the problem is.

Any ideas? I'd like to have a clue about what's causing the problem even if I do end up calling a plumber.

Thanks,

Illyra