Have something on your mind Sorry if I seem distracted I have a lot on my mind today.
Definition to be thinking about something.
Example Number one Janet had a lot on her mind and she forgot her phone at home.
Meaning she was thinking about so many things and she forgot her phone example number two.
I have so much on my mind that I can't concentrate on my work meaning I'm thinking about a lot of things
and it's affecting my ability to concentrate.