Can't stop losing weight

I've been depressed for a long time and I'm never hungry. I try to make myself eat but I just feel sick when I try. I never have any energy and I can't think straight and I know that not eating is just making me more depressed. I just checked and my BMI is down to like 17. How can I break the cycle?

EDIT: Medical marijuana is legal(ish) where I am (not for any medical conditions I have unfortunately) and I already do smoke...it helps more than anything else, but I still can't actually gain any weight. I should try edibles more often. I think it's mostly my anxiety acting up and smoking doesn't always actually help with that.