I have a 3/4 hp sub well pump it was doing just fine a few months ago but now its lost pressure I am now getting about five lbs of pressure out of the well not sure if it's the pump or the start cap how do I tell?

How old is the pump? If the pump is running, then the capacitor would seem to be doing its job. Could be the pump or a rather significant leak in the wellpipe. Also could be a drop in the water table.