Confused

My daughter was diagnosed with epilepsy last fall. The doctors had previously diagnosed her with depression and we dealt with that for a little over a year. It took almost a year to diagnose her after she had the first known full seizure. She was put on lamictal and it has seemed to help but I think she is having seizures again. It is hard for me to know when or if she is having seizures because they are always at night. I believe she is having seizures because I notice a change in her behavior (she sleeps longer hours on the weekends, she is more tearful, her concentration is reduced etc.) My question is 2 fold... Since last year, her teachers notice a lack of concentration after lunch. She does very well in her classes and keeps good grades, all except the class after lunch (last year it was reading and this year science). Should I be checking if she possibly has diabetes or is this just caused by lack of adequete sleep due to the night seizures? My second question is that because her seizures are at night, I don't know how often she is having seizures or how long the seizures last. My understanding is that this is what they base the diagnosis. We had a sleep deprivation EEG but should I insist on a sleep study?