Talk to your psychologist and see how important the diagnosis is to them. For many psychologists the diagnosis is just a requirement of insurance companies so they can get paid. It is also a legal requirement in many states.

Obviously we can't really know if his/her diagnosis is correct based on one paragraph you have posted here. It certianly sounds like you are describing dysthmia (chronic depression). I'm sure there is evidence for a Major Depressive Episode as well. Like I said the diagnosis isn't important. The treatment is.