It's been maybe 10 years or more since I took 300 mg Lamictal, the highest dose I think I took. I never recall fatigue. In fact, it made me hypomanic, then full manic (with psychosis). I was also on Abilify at the time. I do recall sweating a lot, but believe that was related to the manic symptoms.

The main side effect I had when on 300 mg Lamictal was mild cognitive issues (memory issues). They were likely not that bad, though. I also had some anxiety issues.