My mom wanted me to spend more time with her, so I did, but now she's smothering me?

Can you sit down with her and discuss just how much time she expects you to spend with her. You don't say how old you are but I'm sure you have other necessary things you must do - work, school, other activities. Discuss your schedule with her and decide together what times will be her times. Be sure it is reasonable and then devote all your time to her during those periods.