Set goals for yourself and don't best yourself up about not going through with them. Goals are meant to either keep you busy or something that's needed. Also, learn your bare minimum. Meditate for at least five minutes a day, if you have trouble listen to a guided meditation. Keep yourself occupied. Take breaks when you feel the need.

Sertraline never worked for me (took it for about a year). Switched to Lexapro, and I smoke weed frequently. Results are significant.

Talk to your doctor. They are many different medicines. Sertraline is an SSRI (selective serotonin reuptake inhibitor). Sometimes SSRIs don't work for particular people. You could ask about SNRIs (Serotonin and Norepinephrine Reuptake inhibitor) or try something different. I'm on bupropion which is a Norepinephrine and Dopamine Reuptake Inhibitor as well as fluoxetine which is a standard SSRI. It's just trial and error which sucks but you'll find the right meds eventually.