@muffin, the responses from Dan Andrews and backinshapebuddy are the most important things to continue.
From personal experience, the signs of kidney damage really are that subtle that you'll think you are healthy until your kidneys have finally had enough. Also, the foods you eat most likely have more than adequate protein. I was active, ate relatively well, and was pretty fit. However, lack of portion control and too many protein shacks overworked my kidneys causing the damage you're talking about. This was between high school and college, so it was really unexpected.
The problem is mainly consuming too much protein which is very easy to do. Most foods naturally contain more protein than you'd expect per serving. If you live in the US or similar countries, the portions you're used to eating can be multiple servings. The same goes for drinks. Most serving sizes are an 8 ounce cup, but most glasses hold much more than 8 oz. So, you might be getting even more protein through shakes, milk, etc than you think.
Typically, it's recommended that bodybuilders get ~1 to 1.5 grams of protein per kilogram of body weight. Again, that's kilogram not pound. So, for a 160 pound person that would be about 73 to 109.5 grams. Depending on your level of activity, you'll probably only need that 73 which is really easy to get.
I'd suggest limiting the shakes to days when you actually lift. And even then, just one shake tops. And of course, see a doctor if it really worries that much. A general practitioner could probably order you blood work and refer you to a nephrologist if there actually is a problem.
*Edited: you can have kidney damage without ever getting a kidney stone!!! I have never had a kidney stone in my life, yet my kidney function is extremely impaired. I'm not so bad that I have to be on dialysis, but I have to closely monitor my diet to prevent it from getting worse. it won't get much better, but if I monitor my diet(which sucks) I can avoid dialysis and kidney transplantation(which would suck worse)
Tl;dr: It's very easy for bodybuilders to ingest too much protein. Lots of steaks, chicken breasts, plus protein can be overkill if you don't monitor your portions. See a doctor if it really concerns you.