I have hot water when i turn on all the sinks in the house. When i turn on the shower, there;s no hot water. It's barely lukewarm. It's a one-nozzled thingy. Not one for cold and one for hot. What do i do?:confused:

Most all have one nozzel or shower head but I assume you meant one handle does on/off and hot/cold. This is likely a cartridge or ball valve with seals and the hot onlet is plugged with water heater debris, fairly common. Any chance of a picture or brand/model of that valve?