Wellbutrin is very stimulating, at least for me it was and based on some reading i did it is actually somewhat close in chemical structure to things like adderall. Not sure if lexapro is a more stimulating anti-depressant but its possible that combination might increase anxiety.

I know every anti-depressant i have tried thus far ends up increasing my anxiety...though seems like the one was working ok for you, but being on two stimulating meds(provided lexapro is one) could certainly problematic....either way I'd talk to your doctor about your concerns though.