The reason might be that you are just tired, overall, and your body is overly stressed. You could take Glicin, which is a beneficial amino-acid for the brain functions. It is absolutely safe and very cheap, so you are not losing anything with it. Also, you could take Mildronate (Meldonium) – it is very good at boosting one's brain functions and neural recovery. It is used for those recovering from strokes, and for the recovery of athletes. These two supplements would be an amazing beginning. From there on, I would mostly focus on finding the reason of your memory loss.