How do I tell my parents?

I am 16 years old and i have suffered from IBS (an intestinal disorder that causes painful cramping and gastrointestinal issues) for as long as i can remember. It has put me in the emergency room and has hurt my social life as well as school attendance. I have been on multiple medications that give many negative side effects including anti spasmodics and xanax. No medication or treatment has ever been successful in suppressing my stomacheaches. That is untill i started smoking weed. It only takes a few hits and in seconds my problems are completely gone. It also gets rid of my nausea, back pain, stress, and anxiety. I use it daily to stay pain free and happy. My parents do not know i smoke. They are not OK with weed. I can only medicate when they arent around, so any problems i have while they are home, i have to suffer through. I feel that i need to talk to my parents about my situation, but i dont know how to approach it. They really want me to feel better, but i dont know if they would be angry at me for smoking or realize its whats best for my health. I dont know if i should continue medicating in secret or tell them about it. Any advice towards what to do would be much appreciated. Thank you for your time. - RJ