this definitely has to do with the nerve damage. how long ago did you injure your arm?
after my nerve injury (neck & arm), it took me several months to get back to where i had been. right now (after over a year) my left arm is just a tad weaker on the bench press, i can do the same amount of reps as with the right arm, but lack this extra push to finish the movement at the very top on the last 1-2 reps, same story with shoulder presses.
i took ten or so physical therapy sessions and i am still taking massage once a week, more as a precaution against a new injury rather than a fix for the old one.
the bottom line is just be patient and wait. the feeling in your arm should return in time. ice the affected area twice a day, take an ice cube and rub back and forth along your arm until it melts away, go through 3-4 ice cubes, twice a day.