I usally have less LDs when school starts. It could be related to not having the time to think about LDs anymore like Dianeva said. Also you might not be getting as much sleep (either due to school schedule or stress or both) and that could decrease your chances of having lucid dreams since you are dreaming less. Keeping up on your dream journal while at school can help if you arn't already. Also trying too hard to lucid or worrying about it probably won't help your chances.