Is the water pressure also low at other outlets such as kitchen or bathroom sink? If everything is low pressure then you probably need to do the shower head as you mentioned. But, if the pressure on other outlets seem higher, then your shower valve may have a blockage (a problem I had in the past). Normally there are screens installed at the input to the shower valve and they can get plugged up, especially if the condo has done any work on the water lines which can knock loose a bunch of debris (which will collect at the screens if they are installed). The only way (that I know of) to check if you have plugged screens is to turn off the water supply and physically pull the valve off the wall, then turn water back on and see if any debris comes out. Get a Plummer if you are not comfortable removing the valve yourself. Also, did you check with any of the other residents living on your floor to see if they have similar problem?