Talk to Gastroenterologist on Stomach Problem

I have been facing stomach issue from quiet a long time. Most of the time i am suffering from constipation. And then in between i face diarhea. From past a month i am having severe diarhea. Its like i have to go washroom for whatever i eat or drink. I got my all test done before. And they all were clear. Doctor suggested me to go for endoscopy but i cant go for it now. From past a month i habe taken entamizole, ammodium, smecta, bismol, nexium, onset, but still i habe this severe pain in stomach and the stool is tarry with blood. Please let me know what should i do now. I am tired. The doctors never told the actual cause for this.