Plaque forms on your teeth daily. Bacteria in the plaque causes gingivitis – a mild infection. Your gums get red, a bit swollen, or may bleed when brushing. Gingivitis is usually painless. However, gingivitis can progress into periodontitis.  And untreated periodontitis degrades your gums and jawbone even further. You may have exceptionally swollen, painful gums that are likely to bleed.
Your infected and inflamed gums can also result in a periodontal abscess.  Abscesses are a serious condition that can damage your bone and surrounding teeth.  The infection can possibly spread to other parts of the body. You should see your dentist as soon as possible if you discover a pimple-like swelling on your gum.
You should also see your dentist as soon as possible if you also have the following symptoms (even if you don’t have any discomfort): changes in the way your teeth fit together when biting. Changes in the fit of partial dentures. Deep pockets between teeth and gums. Loose or shifting teeth. Persistent bad breath or bad taste in your mouth, or receding gums.
In the meantime, to ease the pain and draw the pus toward the surface, try rinsing your mouth with a mild salt water solution (1/2 teaspoon of table salt in 8 ounces of water) several times a day.