Mothers how to you cope with stress?

I have a 2 yr old and I get so stressed out with him Im a single mother I go to college full time hard to study with at 2 yr old I must say as well...I feel like every 2 seconds Im telling him NO its terrible he gets into everything which I know is normal Im a clean freak I hate messes all I seem to do is clean some days he gets on my last nerve I try to keep him occupied playing with new toys watching movies ect. I have recently started smoking again(I would never do it around him I go outside!!) please don't judge me for that I feel like its the only way to relieve my stress!! How do you cope with your stress how do you keep from going insane some days I feel like Im at my brink always on the edge!!