Dark urine is usually heavily concentrated, which would make it smell more. You need to drink more water.
I looked up Kidney Failure on the Mayo Clinic's website and they didn't mention back pain as a symptom. Unless you're having other symptoms, such as fatigue, low urine output (after you've upped your water intake), shortness of breath, confusion, etc., don't worry about it.
Your back pain may be related to stress.
I know everyone in your life is telling you to stop smoking, but that is a decision you have to make for yourself. If you do want to stop, there are products and support programs out there to help. You don't have to do it alone. I know it's easy to say that you'll quit later, but it will only get more difficult the longer you smoke.
It is especially difficult considering how much stress you say you are under. You need to find a way to reduce that stress, not just to make quitting easier, but to improve your health and quality of life overall. If you have too much going on in your life, ask for help. Take time out for yourself every day, even if it's just 20 minutes of peace and quiet where you can take a bath, read a magazine, or sit outside and enjoy the fresh air. Try not to smoke during this time. Try to learn to relax without a cigarette.
If your symptoms persist, see your doctor.
Good luck.
