Maybe pressure balancer going bad or you don't have a pressure balanced valve
On single handle shower valves, designed to let cold water first and turn handle farther to mix hot water to desired setting. If hot water turned on first, possibility of getting scalded. If seperate hot/cold handles for shower, shower valve needs work.
geyser
Replace the shower valve.
it depends on what your hot water level is
when hot waoter comes out of the shower you made have a water heater
When you take a shower, you're mixing a combination of hot and cold water to make a comfortable temperature for the shower water. A toilet draws only off the cold water system. In older or poorly designed plumbing systems, when you flush the toilet, the cold water is pulled by toilet, so the water coming through the shower is only drawing from the hot water tank.
Your hot water heater is not large enough.
if u take too long a hot shower, ur body temperature will adjust to the temperature of the hot water and its hard on your heart
The plaming tubes are all conected.When the cold water run in kitchen the cold water at the shower become less,so with less cold water at the mix cold-hot (the balance is desterb),making the water hoter.Same if you turn on the hot in the kitchen the water will be colder in the shower.
I get those when I take a hot shower too, apparently it happens when the water is too hot.
A hot shower or immerse the aren and shoulder in a tub of hot water may help pain.
Could be water-heater problems or faulty valve.