Could epilepsy medications be causing low blood sugar or weight loss?

Cause or effect? As a general rule most epilepsy medications stimulate the appetite. Topiramate and Felbamate can decrease appetite in some patients. All aeds may be associated with depressive reaction. Many aeds may affect liver metabolism and may affect sugar metabolism. You need a thorough medical evaluation to look for other causes. If side effects are too much, a trial of another AED would be reasonable.
Yes. Although weight gain seems to be a problem with some anti-seizure drugs for epilepsy, others appear to the opposite effect. According to the epilepsy foundation, a loss of appetite and subsequent weight loss are side effects of some antiepileptic medications including carbamezepine (carbatrol, equetro, tegretol, tegretol xr), Felbamate (felbatol) and Divalproex Sodium (depakote, Depakote er).