Perianal Fistula Surgery. Probl!

I have done fistula Surgery last Friday, Now resting at Home, every thing is fine, but when I go to bathroom for stool I Got Uncontrollably Burning Sensation Even i Cried at that time and After that i am taking sit bath in warm water than i feel relaxation. My wound is open and got Pain Sometimes. From last 2 days I have diarrhoea due to antibiotic side effects but I am really suffering from that Burning sensation so I just want to know how can I prevent that Burning sensation. I am taking Very light food which is recommended after Surgery, no Spicy food, even taking more fruits than the whole meal Still I am suffering from this Situation. I am going for daily dressing and I also asked to my Surgeon about this Situation But he told me that this will happen for almost 15 to 20 days till the new skin is not formed and for betterment he told me for sit bath. Last concern is how many days it Will take to heal that wound.. Please Suggest me Proper way to resolve that Burning sensation Probl