Do you have seperate valves in main lines to bathroom. If you have check them out and make sure they are open and if you have them take them loose and see if the washers are not swelled up, you also might have some lime buildup in pipe. If you have seperate stops under lav. take supply line loose and get a bucket and turn wter on and see what kind of press. you have if you have a lot then you have problem with faucet, if not then problem is the valve are in the line behind valve, you will have to do that till you get to source.
Art retired plbg