Why does under my right vagina lip appear swollen and red and hurts a little ?

Blockage likely: You likely have what is called a "bartholin gland cyst." the Bartholin's glands produce mucus to help defend the vulva against infection, but sometimes can get obsturcted in a similar manner to a pimple. While this is a likely explaination, you should see a physican to make sure it isn't something more serious. The best initial treatment would be a "sitz bath" (warm water 2-3x day).

Possible Infection: Either an infection of the right Bartholin's gland or a hair follicle infection. See your gyn doctor to be evaluated.