I'm on 25 mg of Lamictal right now and I don't feel tired on it... but everybody is different

Apparently sleepiness is a common side effect. See this: Side Effects of Lamictal (Lamotrigine) Drug Center - RxList

"Common side effects of Lamictal may include: dizziness, tremors, sleepiness, loss of coordination, headache, double vision, blurred vision, nausea, vomiting, stomach pain, dry mouth, changes in menstrual periods, back pain, sore throat, runny nose, or sleep problems (insomnia)"