Major Depression?

Been treated for depression with Lexapro for 3 yrs with no therapy. While on the medication had very severe bouts so I started therapy, now 3 months, and changed to Wellbutrin XL, am having some very sad and hopeless days and weeks. My symptoms are I will feel positive, energetic with great plans for the future for periods of 1- to 3 months, then I experience inner turmoil and then I give up, and become severely depressed and hopeless, lasting 1 - 2 months and then it all starts again. During the depressive state, the inner turmoil is what seems to be the worst. I talk myself out of every potentially good idea or thought. I play out ideas in my head from start to finish and it always turns out bad in my mind so I don't even try to do it so I go deeper into hopelessness. Therapist says it may be bipolar am going to a psychiatrist for eval and possible medication adjustment. I am 40, have a good life and yet don't see it at all. I can't anything going I just get by. Any ideas?