Abnormal Stomach Weak digestion.

Today morning I had normal then loose stools after that I felt bitter taste of mouth and nausea. Then after few minutes I had burning sensation in stomach then cramp then again loose stools. After that I am having little bit heaviness in stomach and feeling of going washrum. 2 days back I also had semi digested stools I can see food particles in motions. I am suffering from such problem since more than year which is not getting resolve anytime my stomach become unwell even though I am taking proper hyegnic and normal diet drinking bislery water only. Earlier doctor said it is due to infection now the say it is due to gas. Earlier done infection treatment many times. It is gas or again there is some infection? Pl suggest way to get rid of this I am very much concern not able to live normal life. For few days everything become normal then suddenly such issue occurs like cramps, semi digested, semi solid motions, frequent motions, many time unable to clean stomach ,bloating, Gas, etc