What could possibly cause a person to have either vomiting or severe diarhea when food is ingested?

&the last 23 years I have had chronic severe diarrhea. Now in addition it's getting where if I have ANY food in my stomach at all and I don't get diarrhea I will get pain and nausea/vomiting. Either way I cannot keep anything in my stomach and as a result weigh only 95 lbs. I have been to many gastro Drs. and either do not get a dx. at all or I get an incorrect one for which the precsribed rx's/treatments do not work. I am a 63 yr. old female, and have had every conceivable test available. Is there ANYBODY that could help me? I am so, so tired. Thank You, susan