How To Make Anal Hole Bigger?

Hi, i,m 21 year old male, i have problem of anas pain when i go 2 release my stool, so my mom told me sometimes before she past away. She said that when i was born my anus was closed so the Dc did operation, so now my anus mini for me to pass out my stool because i did operation when i was young, now am old, it is difficult for me to pass out my stool. I live in R.S.A. I need help what can i do to settle this issue?. According to i think to go to Doc and do operation again to extend my anus.