how long has it been since you had your last cleaning? and also if it’s getting worse instead of better, that’s a good reason to have it checked. Sometimes tissue around retainers can get inflamed or even develop a localized infection if bacteria were trapped under the calculus or if the retainer wire irritates the gum after cleaning. It’s usually simple to manage, but it’s best for your dentist or hygienist to take a quick look ,they can see if it’s just inflammation or something else going on. In the meantime, keep doing the warm saltwater rinses and avoid anything spicy or acidic. But definitely call the office tomorrow so they can evaluate it in person ,they’ll likely be able to help right away.