There are multiple conditions that can cause trouble with the muscles, including twitching or cramping and also weakness or loss of muscle mass. As a first approximation to figuring out what is going on, your primary care doctor
would probably perform some basic blood counts, as well as look at common electrolyte abnormalities (which can cause muscle twitches or cramps), the functioning of your thyroid examination, and markers of muscle damage. These tests rule out the majority of conditions that could be associated with the symptoms you are experiencing. If these tests have been negative, which it sounds like they might have been, then you might want to talk with your primary care doctor about whether or not a referral to a specialist for additional testing and evaluation might be necessary.
In particular, certain neurologists
specialist in neuromuscular disorders, which encompass the types of conditions which might cause your symptoms but which might not be picked up on the general blood screening tests your primary doctor has already performed. At a visit with a neurologist, they will pay close attention to defining whether you have any objective muscle weakness, or other evidence of a nerve problem. If so, they may wish to perform EMG
testing to further explore what might be going on.
Good luck, and please speak to a doctor soon.