I cant cope please help?

i cant cope any more. i am a single mum of four kids aged 13, 11, 8 and 4. the older two are boys, younger two girls. the girls are no problem, they have thier moments but the oldest boy gives me so much verble and physical abuse he steals money from me,beats his brother and sisters up. he has asked me to put him in care a lot recently, i dont know what to do anymore, part of me wants to put him in care but if i do im scared he wont come home or the social services will take all my kids from me. my 11 yr old son has behaviour problems but has been to see paeditions but they say he is fine. i dont have no help with my kids thier dads have not seen them for several yrs now. i have been to my doctor and cried and begged for help but they dont want to know they say i should be able to cope. i cry most the time if im not crying i am hypo and cant stop talking! i hear vioces in my head some nights. i feel like im loosing my mind. my own mum and dad divorced when i ws 12 i see my mum rearly she dont want to know or help, my dad is ill so cant help. i dont know what do do anymore.