I think I sprained my ankle three days ago. The ankle has remained swollen even now. But it doesn't hurt at all -- just a little tender.?

Try some RICE. Rest, ice, compression, and elevation should help. Additionally, for the minor pain, Acetaminophen or an anti-inflammatory drug like naproxyn or Ibuprofen can help.
Ankle sprain. Sprains can take weeks-months to heal. Swelling may persist few days, especially if you've walking on it & not elevating it as much as possible. Use ice first 24-48 hrs to help reduce swelling; then can try alternating ice & heat, but if swelling worsens, go back to ice. If swelling worsens or ankle becomes more painful, see pcp for further evaluation. May need airsplint or cast.