I have a single handled shower stall and the pressure is really low and only get hot water from it. Not sure what to even check, as it appears it is just affecting my shower faucet. Please help

Since it is hot only, the most likely culprit is debris trapped in the inlet ports to the cartridge or the cartridge itself. Only thing to do is shut off the water to the shower, pull the cartridge and see what you find. Let us know. If you can tell us the brand of the faucet, we may be able to offer more help. You Tube is another great resource when you know the name.

... and once you did what ma0641 suggested - before you turn water ON, remove shower head and clean filter screen inside the female thread of shower head . Now, turn water ON, run it for a minute without shower head attached, then, reinstall shower head

Today's shower faucets are temperature and pressure balanced. There is a good chance the temp-balancing device inside the cartridge is not working. You may have to replace entire cartridge.

Hope that helps

Milo