More than likely a blockage, leak, or bad installation.
If some other showers, toilets, and sinks are having problems with running water then it's likely a problem with the entire water system, usually bad parts or a leak.
Diagnosis ....
If water pressure is good everywhere else, and the recent pressure seems to have changed, probably cleaning your shower head filters.
If never had good pressure but do everywhere else, you may need a lees restrictive head or shower valve, or your piping may be corroded.
Pressure is not the same as volume.... Most people say pressure when they want volume. You can have the same pressure to take a shower that comes out of a squirt gun, or one that comes out of a fire hose... The difference is the volume of water that makes the biggest difference. The answers above are mostly volume related.
call your plumber, he could help unstop your gerbil from the shower pipes
or pay the water bill
Clean the shower head of mineral deposits
you have trash in your line take the shower head off and remove trash or possibly in water valve at shower
Maybe pressure balancer going bad or you don't have a pressure balanced valve
Hot water is spraying out into the atmosphere at high pressure. This causes condensation.
Well, if you take a shower with hot water, it should get worse, since a hotter temperature increases blood pressure....
This is probably a pressure imbalance problem or you have air in the lines. see the related video link provided.
A stuck or worn balancing spool in a pressure balanced valve.
My first thought is a leaky hot water line.
The pressure of the water is defined by the weight of the water pushing down as a result of gravity. If you're hot water tank is full then the pressure will be high and the hot water will gush out, if there is little hot water then the pressure will be less.Also, if you live in a hard water area then the shower head might be clogged with limescale. Try cleaning your shower head if it is covered with a thin scale.WOW I never heard such nonsense1- If the shower head was clogged with scale then BOTH hot and cold would diminish 2- If the hot water tank was not full of water and had air in it the pressure would actually INCREASE as the water is heated as AIR can be compressed and water very slightly increasesEver take a balloon fill it with air and pop it?Now try it with water it plops openThe low water condition could be a washer blocking the orifice by the valve seatYour only condition is one fixture so the other persons advice is totally wrong
Run a new cold supply line from the source. This will drain less pressure from the the cold shower line.
The piping has to be the exact same length for each shower head from the tee where the cold and hot water feeds from the top of the diverter faucet.
Open up the actual shower head and remove the factory fitted restrictor.
Because hot water can raise your blood pressure rapidly. Otherwise you'd be refreshed and energetic.