Why am I so forgetful?

During school I left my folder at different places in the same day and had to go back to get them. I think my memory has worsened and I'm forgetting things. I have to wake up early for school, so I don't sleep as much. But I don't think thats the case because it didn't use to happen. I've had a really stressful time lately too but what other reasons could be the cause? Please explain. Thanks.