I have personally developed the Lamictal reaction rash by upping my dose of Lamictal from 250mg to 300mg. After this happened, my doctor removed me from the medication immediately (which turned out to be the wrong move [tapering down would have been nice]).

If you believe you are getting the rash because of an increased dose of Lamictal, I recommend you call your doctor. But don't let them hose you like they hosed me.