I had extreme pain in my kidneys accompained by nausea. 2 days later i found blood in my stool. what is this?!

Probably not kidneys: Your pain was at the flanks, but not necessarily in the kidneys, per se. Pains in the middle of the torso can refer to any of a number of organs and tissues. If there was blood in stool, and it was related, the problem was from the G.I. Tract, with which the kidneys do not intersect. The color of said blood can determine the level of the origin within the G.I. Tract. Black= upper; red = lower.