What is the cause of thumb stiffness, muscle pain, and body twitch?

Hello doctor,

Two months ago, I first noticed my right-hand thumb being stiff when using my phone. It subsided after a few minutes and returned to normal. A few days later, while sipping a cup of tea, my thumb began to feel stiff once more and to shake somewhat. I began to worry then. I struggled for 10-minute to grip a pen two weeks later. My grip then returned to normal. Since this episode a few weeks ago, I have not experienced any grip problems, though occasionally, my body does feel stiff and lethargic. Could this be the beginning of weakness? Throughout this time, I have been experiencing some pain in my arm. At times in the wrist, other times in the forearm. Pain has radiated from my neck to my shoulder area at times. I have noticed my right hand, which is my dominant hand, being weaker than my left hand, for example, lifting buckets of water. As my right hand is my strong hand, and there is a slight difference between the size of the thumb muscles in my two hands, I am concerned that they are atrophying. Could atrophy happen so soon in ALS (amyotrophic lateral sclerosis)? Would I still be able to do regular things, albeit finding it more difficult? Most worryingly, I have also developed twitches all over my body. Both arms and legs, but mostly the right side of my body. I have even felt it in my eyes and nose on occasion. I have been experiencing anxiety lately and wonder if that is a factor. Would twitches come this early in ALS? I am very anxious about having ALS symptoms. I consulted my GP (general practitioner) doctor three weeks ago. All balance, strength, and reflex tests were good. He booked an MRI (magnetic resonance imaging) and blood tests as a precaution. My MRI came back normal. My GP has referred me to a neurologist, and an appointment will be weeks, if not months. I am curious whether these initial ALS symptoms observed, have been reported in positive cases. Please help.

Thank you Dr. Aida. The pain along my arm and wrist has subsided and I hardly notice any issues there at all presently. Could this have remedied itself on its own? My main concern would be the twitching which I feel mostly in the muscles of my right leg. I feel them in many other places too but that's where its dominant. These are constant throughout the day and have been for many weeks (possibly 6 weeks). Could this be an inital symptom of als in patients? I have read many posts online and I admit most of them have worried me. Thanks