Sometimes opening the hot valve all the way, then closing it very tightly, and repeating this about ten times, can crush and flush the sediment and minerals that are collected around the valve seat and/or the sealing washer.
A slow-dripping faucet will collect crud inside like that.
However, if the old washer is breaking up (which can cause this slow trickle), this procedure can cause more chunks of the old decaying rubber washer to go bye-bye.
Probably time to scrimp and save somehow, live on peanut butter sangwiches and ramen soup for a week, and get a plumber out there.
Or talk to neighbors and co-workers, see if any are handy enough to try fixing it just for pizza and beer.
That old valve might be so rocked in there from minerals that it will be tough to get it apart to service it.
When it finally gets fixed, you will pbly want to remove and flush out the crud from your shower head, if your tub has one.