I had my tub removed and had a walk-in shower created in late Jan. The water temp. began to get cooler in March. Now, it is frigid. The hot water streams out of the sink, and none of my neighbors in my condo building are experiencing problems with their showers. So, I don't the water heater is to blame. What could be causing this problem? Should I contact a plumber or the men who installed the walk-in shower?

What could be causing this problem? Should I contact a plumber or the men who installed the walk-in shower
I would contact whoever installed the shower valve, ( what's the name brand of the valve?) Sounds like you may have some trash blocking the hot water inlet ports of the cartridge. If it's not in warranty do you want to try fixing it yourself? Tom