ouch!

My sit bones hurt!!! Anybody know what to do to help this? I went on a nice long trail ride yesterday and I borrowed a horse for it. I used his saddle which is ancient and had no cushion, which was normally not a problem because the horse was usually very smoothe and slow, but I guess I bounced around more than I realized, because I can't sit up right now! Anybody know what's best for this? I'm supposed to go ride again on Sat, probably the same horse with the same saddle >.<