I need to move out but i'm not 18. Advice?

I'm a 17 year old girl turning 18 in 3 months. I'm in full time education in sixth form and have a part time job but have suffered from an anxiety disorder for many years and battle with depression. My job pays for all my travel, occasional rent for my mother when i can afford it, my food (lactose intolerant meaning my food can be too expensive at times for my mother) and all my clothes, shoes, makeup and any trips/days out i have. At 13 i was forced to move from the flat i comfortably lived in with my mother as she struggled with a breakdown and has since been on long term sickness. The flat we have lived in since is much smaller with a community that i feel uncomfortable around due to my anxiety and also meant my cat who helped calm me had to be re-homed due to the no pets rule. I can't stand living here any longer, it has caused insomnia and my anxiety is getting worse despite years of therapy, meaning my panic and anxiety attacks are increasingly more frequent. I need to move out, have my own place where i can deal with my health as my mother does not understand the severity of my struggle as she has her own health to consider and often makes it worse as she has days where her own depression is a problem. I don't know what to do as my part time job does not pay enough to support my own place on top of my everyday needs even if i was old enough to rent, i'm willing to change jobs and get a shared tenancy with a 19 year old friend (a legal way for a minor to rent) however we do not know how to go about this and i don't know what support i can receive. I wish i could wait until i turn 18 but you have to understand that this situation is jeopardizing my exam grades,my friendships, relationship and my own mental and physical states. Has anyone got any help or advice for me? It would be greatly appreciated.