More Kidney Pain on Day 15

Hello,
I've been doing The Master Cleanse for 15 days now without any bp shakes and sticking just to the salt water in the morning, lemon juice and water in the day and senna tea at night. Before I started the cleanse I was taking lots of drugs, alcohol, smoking and very much addicted to my espresso. I'm a little worried because I have been reading other peoples experiences and mine are nothing in comparison. I’ve had no headaches or mucus or coughing or anything indicating that I’m expelling waste! I’ve been feeling great and still having the energy to cycle around town...Until a few days ago when I started having excruciating pain in my right lower back. I suspect my kidney area. It starts at 12 in the afternoon and generally goes away in night.Last night this pain was so intense that it made me nauseous and I felt like I was coming down with a fever and flue. In the middle of the night I woke up in a massive sweat but no pain. But this morning it's back to feeling fresh and normal. So I’m wondering what this pain in the kidneys is all about and should I stop this cleanse now before it gets worse. I’m not sure if I should drink more water and less lemon or vice versa. I replaced the swf with senna tea in the morning for the last two days but the pain is still coming back. I was aiming to do this cleanse for 20 days but now I don’t know if I should give up or am I just starting to feel the toxins coming out. If I do continue to day 20 should I change anything in the cleanse?