I'm sure you've been told that "feeling weak" is not a symptom of ALS. In ALS, motor nerves are destroyed so that the corresponding muscle cannot be activated. It doesn't feel tired, weak, or exhausted, it just doesn't move.
The "symptom" of reps burning on the left is a good sign. First, ALS wouldn't net you do a single rep, and second, ALS doesn't burn. That's not anxiety related, that an inflamed tendon on the bicep. Take motrin for 3-7 days and it should clear up.