advice on medication for concentration for non-diagnosed

I am currently taking wellbutrin as antidepressant and for concentration (I was not able to read even one paragraph without being distracted mainly by my thoughts but really anything, not able to finish essays, making mistakes in simple tasks, forgetting something at home and having to go back four flights of stairs, losing focus even while having sex, losing things, cards, keys, locking myself out, etc.) but the psychiatrist decided to eliminate the possibility of depression - of course the problems that I mentioned made me sad, but the core problems is focus.

I was very satisfied with wellbutrin for a month or two, but it feels like the effect has worn out: my energy level is low again, motivation and concentration suffer too bringing me back to where I was. My psychiatrists underestimate the severity of my problems with concentration as I was not diagnosed with ADHD as a child, and probably sound like a junkie who wants to get her hands on stimulants by simulating its symptoms. I am a student, and for complicated reasons deferral on the basis of mental health is not an option. I *have* to graduate *this year* and inability to complete the tasks frustrates me leading to high level of stress and bad mood.

I am not aware of the possible lines of treatment and as I said, the doctors are not willing to address this problem. I would be happy to receive some advice on what other options are there, before I try to find another psychiatrist. Thanks!