When a new student approaches me with the problem of quickly re-injuring themselves (as in your shoulder), I always suggest they look to another martial art or type of training for a long while. Perhaps aikido isn't right for them. I know the lure of the culture is strong, but immediate injury often points to chronic reinjury, which leads to frustration, and then anger.
Aikido does not have a monopoly on the powers it promises, or the wisdom it promotes. Listen to your body.