have a lot on (one's) mind
To be mentally preoccupied with many things, often resulting in feelings of unease or agitation. I'm so sorry I made that stupid mistake—I've had a lot on my mind these days. Are you OK? You look like you have a lot on your mind.
have a lot on one's mind
Fig. to have many things to worry about; to be preoccupied. I'm sorry that I'm so grouchy. I have a lot of troubles on my mind. He forgot to go to his appointment because he had a lot on his mind.