I agree with Twin.
Also - check carefully to see if anything has changed. For example, did you replace the filter (could be the wrong size) or have you acid washed the filter (ruins it unless you de-grease it first), or is the filter simply plugged (could look like new, but be coated with oil, which is clear). Clean the filter with an actual 'Filter Cleaning' solution of some type.
Is the water level low, so that the pump pulls air in?
Is there a skimmer door that may be stuck or sticking?
Is there a suction safety of some sort which has failed?
HTH