Do doctors really know what they are doing?

I am only 19 years old and I suffer from manic depressive disorder, psychosis, and endometriosis. I have been prescribed over twenty different medications, which made me too “zombi-fied” to go about daily situations. And eventually, I became immune to each of my medications, having to stay home. I couldn’t attend school for days, or any other extra curricular activities. I use to be in so much pain, mentally and physically, I decided to give up, until a mutual friend heard how I was coping with my situation and suggested I try cannabis. I denied it, “it’s not legal and doctors know what they’re doing” I said. I was having a bad spell one day and decided to hit a bowl. I mean, why not? I’ve tried every other scientifically altered medication, why not herb too? I would say at least 5 minutes later, I was relaxed beyond relief and still able to function for the first time I can remember. Ever since, if I have a bad flare up or feel as if I’m sinking back into the depths of my ‘disorders’ I take a couple drags and I feel uplifted and hopeful. Why should we take medications on top of each other EVERY DAY, when we can create another medical branch to stand alone one to use OCCASIONALLY?