You are using more water than the pump can deliver. You need a larger gpm pump IF the water source, usually a well, can produce it.
If the pump came on at 30 and the pressure rose, you wouldn't have a problem because that is how the system is supposed to work. The causes of the pressure falling below the cutin when the pump cmes on could be improper air pressure in the pressure tank, a blocked injector in the pump if it is a jet pump or a bad impeller in a jet pump of a worn out submersible pump or water leak in the water line from it to the pressure tank. So, what type pump do you have; a sub in teh wel or a jet above ground somewhere?