Wellbutrin and girlfriend

This is the 3rd time I have been on Wellbutrin. Once in 1999, then in 2004, and just started taking it again 3 months ago. The first two times I took it I had joint pain and a lot of muscle inflammation. This go around is different... Just recently, within the past few weeks, I started breaking out with hives, after taking it with no problems for three months! Started on my head and progressively got worse. I break out all over my body, head, legs, back, hands, etc. For some reason it seems to happen more frequently when I lay down in my bed to go to sleep (weird!) One other scary side affect is, I frequently stop breathing when I start to fall asleep, and wake up gasping for air. Has anyone else experienced this?
Since I had never experienced problems with hives the first few times I was on Wellbutrin, I didn't think it was the medication causing the hives. So, I cut my dose in half (50mg/day). The hives didn't go away, so I stopped taking it all together 3 days ago, but still continue to get hives. Does anyone know how long it takes to get it out of your system?