Start with internist
An internist is a general practitioner. Problem could be caused by medication causing low potassium
, not drinking enough fluids, overusage of muscles, a muscle disease such as pmr etc.
If internist can't find cause, consider a physiatrist (specialist in entire musculoskeletal system); or rheumatologist (joint and muscle diseases)., generally, drink more water, eat lots potassium rich foods (fruits).