I started to feel pain while sitting and later i found out that my outer lip (only 1) is swollen. it has purple-redish color. its not filled and it doesnt look like a pimple. its not itchy, just painful to touch. what can it be? how can i treat it?

Tentatively, just apply cold compress 10 minutes, 3-4 times a day for pain alternating with warm, baking soda sitz bath ( 4 table spoons of baking soda in 2 liters), 15 minutes, 2-3 times/day, for a day or two. If symptoms get worse next day and other symptoms develop, such as vaginal discharge, dysuria, etc.), you should see your doctor by then.