I've noticed a fine constant movement in on my right lower bicep. doc said it was fine but i notice when i use the arm it gets tired fast. is it als?

Fasciculations: There are several causes for muscle twitches including too much caffeine, hyperventilation, nerve root irritation and most commonly 'benign fasciculation syndrome'. Als would not selectively involve one muscle. A good neuro exam would go a long way in figuring this out. I have never seen ALS in a 20 yr old.

Arm: Based on age and symptoms this is very likely not als.

No: You may have a nerve issue afflicting your biceps, such as a pinched nerve in the neck at C-5, 6, or maybe a bicipital tendon issue. You are NOT describing ALS