Prolonged Constipation. At end of anus.

I have been suffering from constipation since 6 months. When I 1st consulted the doctor, he prescribed some medicines and pointed out that it could be because of Vitamin B and D deficiency. After that I am able to bring back the Vitamin B and D to normal level in my body using medications. Though there was no improvement in my condition it was gone after 1 month and again after 2 months it has come back and this time I have normal ranges of vitamin B and D. I visited another doctor, who did Sigmoidoscopy and told that I don't have any problem in results and recommended me to take more fibre content, consume more water and to not eat any non-veg foods. And it been 2 months ,Despite the diet change I don't see any improvement and it is becoming more problematic. I am not at feeling normal in my stomach, I am having incomplete bowels, very hard to stool which leads to bloating and gas formation. I feel like it is accumulating and stuck at end of anus.