Your dog could be suffering from anal gland abscesses or fistulas, This is painful and should be seen by a veterinarian. The hair will need to be clipped, the anal sacs need to be checked manually, and if abscessed they will need to be lanced, evacuated, flushed and infused with an antibiotic ointment. Since this is quite painful your dog will also get some pain medicine. Please take Osito to the vet tomorrow.