lingyai

I'm a 47 year old male in generally good health (so far as I know). A week ago I started exercising on a mini trampoline. Nothing too intense -- sessions of moderate intensity for around 15 minutes each, once a day. Felt quite good afterwards. But on the fourth (consecutive) day, in the middle of the session, I started feeling a pain in what I believe are my kidneys (on either side of the top of my lower back). It wasn't too bad, so I finished the session. But afterwards, they kidneys (if that's what they are) kept hurting, the right side more than the left. Not severe, distracting pain, but I was aware of it. I took a 48 hour break from the trampoline, and meanwhile drank lots of water. Urine was/is not discolored or funny-smelling. The discomfort was very mild and went away completely about 36 hours into the break. Anyway, I ended the 48 hour break today. Almost immediately when I started jumping on the trampoline, the pain returned. It was fairly sharp. I decided my body was trying to tell me something, so I stopped jumping. No residual pain -- but this worries me. Any idea what this could be?