It's due to gum sweeling. It may be due to any kind of infection
. Not necessary it is a sign of hiv
. Soo dnt worry. Maintain a good hygiene of your mouth. Wash teeth 2-3 times a day. Brush at night with baking soda. Rinse your mouth with lemon water. Boil few leaves of guava with water. Then rinse your mouth with that water. With this you need homoeopathic treatment. U can also contact me through Lybrate.