My son was diagnosed with ataxia.....the doctors really don't know why my son can't walk and hold his balance.

yesturday afternoon after he woke up from his nap he had seemed a little unbalanced. he went to play with a toy that you can ride on him and the toy fell backwards and ever since then he hasn't been able to walk nor hold balance. on the way to the hospital he had up-chucked and then he done that two more times at the hospital and once again back at home.

That is bizarre, but you really should get him to see a neurologist RIGHT NOW do not wait, it could be some kind of brain injury. It almost sounds as if he hit his head when he fell and could have gotten a concussion and could have bleeding in his brain or something. Did the doctors run any tests? Either way it is probably your best bet to get him to a neurologist so he can be diagnosed and treated.
vomiting once or twice after a head injury is normal any more than that is very worry some indeed. When my son hit his head recently the doctor said that if he puked any more than twice that it could be the sign of a serious problem.
Let us know how it turns out

the balance part may be an ear infection, but up chucking and stuff like that may be something else.

as bizarre as it sounds, the ear holds the key to your balance.