Honestly, your symptoms sound almost identical to mine! I think you've answered the ache in your left arm, from holding your son all the time.

Twitching all over I can assure I have had! It's so frustrating because once you feel one twitch, it's as though they don't stop but they will, trust me. The ALS hole is a very easy one to get stuck in because of the severity of the disease but it is very rare.