Hi Marcie!
I take Lamictal. And I have trouble concentrating. I didn't notice the side-effect at first, because I was in school and didn't have to work eight hours straight. I could take breaks whenever I wanted, for as long as I wanted. But after graduation, I discovered I only could concentrate about four hours a day. My doctor recently prescribed some ADHD meds to offset the effect of Lamictal.
Don't know how long you've been taking the med... I started it in March of 2003 and was slowly weaned off of Lithium, while taking more Lamictal, until July 2003. Sometimes it takes a while to work. Personally, it was so worth it to me... I've lost over half the weight I put on when I took Lithium, plus I no longer have to sleep twelve hours a day or take anti-depressants.
Hope you find what works for you.