balance problems and Dr's can't figure it out!

In recent years,I've developed balance problems,and I have been to several different kinds of doctors,and had different kinds of tests.All the doctors couldn't figure out what was causing it,the neurologist I was seeing said he was out of ideas and suggested going to Emory(I live i south Georgia)The different types of tests I've had include an MRI,x-rays,bloodwork,tilt table test and others,but they didn't show anything.I can't walk a straight line,can't draw one,I've almost fell over several times,and I walk like I'm drunk,though I don't drink!When they've checked my blood presure,it was good at the time,but my feet are always cold,when I bend over,it looks like my head will explode.I wake up with headaches every morning,I was diagnosed with sleep apnea,and use a CPAP machine.I'm tired of spending money,just to be told "I don't know what the cause is"Can someone tell me what might be causing this,or tell me something to put me going in the right direction?