No, it is definitely not a matter of accepting it. When I feel like I am not contributing I find a way to be genuinely helpful, and the feeling goes away. It also helps if I accomplish something for myself that has real value.

Doing things differently will most likely help you. However, if no action you take alters your thinking, you could have a more serious issue.

What exactly HAVE you done? Other than the drugs? Did you try to volunteer, or something like that? It's well known that drugs by themselves rarely fix serious mental problems. Look into cognitive behavior therapy.

Whatever you do, do not wait for it to go away. The deeper your habits of thinking entrench themselves in your brain, the harder they become to control. Of course, there is a chance that this is a "phase", but you should not risk that. Teenagers can suffer also, it annoys me when teenage problems are dismissed as normal.