Have you been checked for a pilonidal cyst? Pineal cyst comes from the tail bone. When they do surgery, they need to follow the trail because a Peinado cyst travels.
The doctor needs to do more than just drain it, they have to go in deep and track it.
I had one that kept reoccurring, but it was nowhere near the tailbone, and then my surgeon tracked the infection to the tailbone and was able to heal it.
All the best to you, I hope they can get you taken care of and this helps.
Wow, that's so long to deal with this. I assume you have gone to the doctor to inquire? You need to. What comes to mind is an anal fistula. https://www.mayoclinic.org/diseases-conditions/anal-fistula/symptoms-causes/syc-20352871 Do you do sitz baths? This unfortunately does have some invasive strategies to get rid of it if it continues. When you have the pus, do you have other symptoms of infection such as fever, heat and pain?