You didn't mention about the Drugs that you are taking now.If are taking any Antibiotic or pain killers,they may cause Nausea
If you are experiencing Diarrhoea
immediately after eating,it may be Irritable Bowel Syndrome(IBS).Burning sensation radiating from lower abdomen to pelvis needs to be investigated.Please consult your Local doctor
and get investigations like Upper Gi endoscopy
I can review after the reports.