Have you looked up the symptoms of an anal fissure? It sounds like that may cause such burning and stinging you describe. If such a fissure is located inside the anal channel, it burns if an undigested piece of food (like nut pieces) gets stuck in there.
If so, you could try to flush it out with a strong water jet (bidet or shower). Or carefully examine with a finger and a non irritating gel like petrolatum.
When I had such a fissure, I could tolerate it during daytime when I was busy, but it was difficult at night when I could not sleep because it burned. An enema with water only was also something that helped me in that situation (as I thought for several weeks I would suffer from an interior inflammation like cuffits).