Black stool stomach burn/pain low bp gas

Problem started last Monday with fever weakness dizziness(low bp) black stool stomach burn. Dr suspected of dengue/typhoid but tests were -ve platelets normal. We changed 3 doctors nobody can rectify problem. 1st diarrhea with black stool then after medication stool was normal for 1 day then little green stool (no diarrhea) then black stool (no diarhhea) but stomach was not getting clear very little stool passage & now again its yellowish brown stool but dizziness is there. Mild abdominal pain is there, a lot of gas & dizziness (low bp) is also there. IVF is helping bp but then again it becomes low. 1st day the bp was 90 then in between it was 100 then 50 then 114 and yesterday it was 90 since last Monday. Whole abdomen endoscopy was normal cbc- basophil count 0.01, monocyte count 0.14 esinophil 0.3 red cell width- 47.8 & 14.3 ESR- 55 Serum globulin- 3.5 rest was normal. What are possible suspects please help. Nobody is able to clarify our doubts. Have changed 5 docs since last week.