I too was very irritated on Wellbutrin alone. I was on Lexapro 10mg first, and felt great emotionally, but I was hungry all the time, couldn't think or concentrate on anything, the sexual side affects - etc. So, my doc switched me to WB. I have been on 300mg since August. I too had trouble sleeping and was staying so angry and irritable, I added 5mg of the Lexapro back about a month ago, and I feel GREAT!
Some people are fine on Wellbutrin alone, but I have heard more with the opposite affect and have to have a low dose of a SSRI along with it.