Wellbutrin may still be working, but not giving you the kind of "high" you described in the beginning. Instead of adding another medication, you might try working on the the everyday problems in a new way, maybe with the help of a therapist,maybe on your own. If you want some help with that, go to www.masteringstress.com.
Higher doses will not give you that same high, nor will
lexapro.
Sounds to me like you're basing your stress and anxiety level on pills, and not the problem at hand. That's not healthy at all. You didn't indicate any anxiety/depressive problems, so why are you complaining about the medication not working? No wonder why you're doc was puzzled...med's like Wellbutrin are not made to make people "high"...