What are signs of kidney problems?
People with kidney problems usually notice a change in your urine production (less or more), change in urine color, or change in urine odor. Also, if the pain you describe actually comes from a kidney, you will develop tenderness on your flank- the spot on either side of your spine below the ribcage on your back. This will really be noticeable if someone makes a fist and taps it (not too hard) on either flank.
To be honest, there are many things that cause pain in your back that radiates to one side. Typical causes are back problems, arthritis, or ribcage problems. Since this is going on for two weeks and you haven' t found the reason, you should probably get it checked out by a healthcare professional.