Your kidneys aren't actually all that sensitive when it comes to actually feeling anything; they usually create some sort of referred pain (for example, if you get hit in the kidney and your left leg hurts like a mofo for no apparent reason - just an example of referred pain). If you're feeling pain in the kidney area (right at the bottom ribs, slightly rearward) then there's most likely something SERIOUS wrong.
From a 12-week cycle, especially if you've retained significant water, your blood pressure - or at least your systolic pressure - was probably wicked-high for some prolonged period of time. This can easily damage the glomerulus of the kidney (the primary pressure-mediated filtration component). If it damaged enough glomeruli, you'd definitely have significant pain either with or without visible blood in the urine. In many cases there actually IS blood in the urine, but it's not detectable because of the dilution; who's gonna see 0.5mL of blood in 1,000 mL of piss, right?!
My advice : see a doctor ASAP, preferably a urologist who will likely be able to give you a rapid and effective diagnosis. Failing that, see an interal specialist. Your G.P. will just send you to one of those two anyway. If you want to become very high-profile, just go to the ER.
Best of luck, bro!
-M