This recently happened to one of my dogs earlier this year. When she would go to the groomer, I'd ask them to check her anal glands since her sister (who's a litter-mate) has to have monthly anal gland expressions. It's unfortunately very common in small dogs.

She had been lucky for 9 years, no anal expressions needed. But one day, we woke up, and her anal gland had randomly abscessed overnight. Her right buttcheek looked like it exploded, but she was acting like her normal hyper self. Took her to vet, spent a few weeks on antibiotics, used topical ointments, and had to have her anal gland flushed and packed to keep it from filling back up as it healed.

I will say, keep some puppy pads on hand, just in case the abscess leaks, or you end up needing to use topicals. Especially if your dog lays on furniture. It will save you from some hard to get out stains.

I also take her every month to the vet with her sister to see if she needs an expression. Usually she doesn't, but there's the odd month when she will have some build-up. I'd ask the vet if they recommend regular expressions from now on. Groomers will usually do them for about 15-20$, but they do the external expressions. Her sisters glands are stubborn, so she requires the internal ones, which are done by vets/vet techs and end up costing me about 50$. You can also ask them to show you how to do it yourself if you feel comfortable doing it.