Hello and welcome to Healthcare magic.
Its been a while, more than 70 days, since the procedure was done. And if it is still painful then only sitz bath with iodine
may not prove to be a good idea.
The cause for this pain can be anal fissure
or a non healing part (iodine has the potential to damage the granulation tissue and hence some what delay healing especially when applied directly as has been done by you) of the wound left after fistulectomy.
So at present the best approach would be to get examined by a doctor (some thing I am unfortunately crippled at and hence can not help you with).
In the mean while if you have pain while passing stool, you can use lignocaine ointment, available over the counter, 5 minutes before going for defecation. As that would not only prevent pain but would also help prevent any worsening of a fissure if any.
Please let me know if you have further questions