Perianal abcess ,treated surgically almost 2 years ago with persistent discharge and non healing indicates fistula formation.You have not given any information about the gap of 2 years and still not seeking re examination by your surgeon.
Recent onset of pain and redness perhaps due to reinfection which needs antibiotics at the moment.
Next Steps
get re examined by your doctor ,you need MRI study of anal region to see the tract.
for time being you can use ciprofloxacin and metronidazole