What you describe could be fasciculation
- which could be normal....
There are several possible investigations in such situations - Serum electrolytes, parathyroid
hormones, ENG, EMG (electrical activity of nerve
or muscle) and so on. They are costly and cumbersome.
Your treating doctor will be able to decide depending on clinical evaluation and other findings.
May be you won't need anything - with time, everything may settle down...