This is an undiagnosed new problem with uncertain diagnosis, and 99213 is likely the appropriate code for the visit.
In this medical scenario, the patient is experiencing leg cramps, and the exact cause is unclear. The physician suggests trying over-the-counter magnesium and potassium supplements to address potential electrolyte imbalances or other contributing factors. Additionally, the recommendation for a scheduled physical and lab work indicates a need for further evaluation to determine the underlying cause of the leg cramps.
Given the uncertainty in diagnosis and the initial approach of recommending supplements rather than an immediate specific treatment plan, it aligns more with an undiagnosed new problem, and a level 99213 evaluation and management code is likely appropriate for this visit. This code reflects a low to moderate complexity visit for an undiagnosed health concern.