my 15 month wont stop bitting

my 15 year old boy bites all the time at home and at day care. the children dont even have to do anything to him he will just walk up and bite them. he also does bite in frustration when he dosnt get his own way and even bites himself sometimes. he has also bitten me and his father. the daycare mums are saying if he dosnt stop i may have to take him out of care (which means i have to quit tafe and work) as he is breaking the skin and even bruising the children. we have tried everything elimntion, smacking, bitting him back, putting him in the corner or  the cot, yelling at him you name it we have tried it. the doctors told me its my fault and i need to learn to dicipline him. both him and my 2 year old have also got a very bad temper which im trying to control but they are verry. stubon and it is very hard i dont know what to do someone plese help i cant afford to quit work cause i wont be able to survie.