Hello and welcome
The opening near anus is mostly a fistula if it is discharging. The discharge may be a clear fluid or a pus. Other possibilities is that it may be a sinus infection
or a superficial wound which can be treated by the use of a oral antibiotics
or antibacterial cream application.
Feel free to consult your doctor and your doctor will tell you by clinical examination that what treatment is best for you and what precautions you have to take in future.
Hope this will help you.
Best Wishes and get well soon