S.R.
I have never used that medication. The med I take for seizures is Noroton (sp) and I know you can't take that with a baby. If the greatest concern is a rash spreading to your baby from you, you could consider pumping milk for your little one and see if your medication appears to affect him.
I did look it up on Web md, and it says it is a common med for Bi-Polar and Seizures. It also list side effects and other info. http://www.webmd.com/epilepsy/lamotrigine-for-epilepsy I hope that link appears for you to click on.
Best of Luck and I hope it all works out.