I Was Snorkelling, A Wave Hit Me, I Fell On

I was snorkelling, a wave hit me, I fell on a "flat rock", I say this as there was no skin cut: It was very
painful: The rock contacted me on the lower spin [back]. I am able to do all activities but it is painful to touch or lay on. I have to sleep on my side. There is severe bruising, a fairly large are just at the "crack" on my lower back and spreading from that area. While this is bruised about 5 - 6 inches above this area my back is
sore (stiff ??). This occurred about a week ago and does not seem to be getting any better:
Thanks