How To Treat An Injured Thumb?

My thumb feels like it is sprained. It popped yesterday, five days after originally injured (trying to twist the end off a hose, with finger taped to a splint). Not positive how I hurt it, possible while boating. I can move it, no crackles. But to use it w any pressure, like using a knife to cut veggies, or to hold something, it hurts. It is sensitive to even touch the spot of the largest bump (hard bump/swelling). It was swollen more, most gone down, never any discoloration. I understand a sprain or legament tear, but the sensitivity to even touch the skin completely baffles me.