Severe Lower Left Back Pain?

That sounds like a kidney infection. They're not dangerous unless left untreated for a very long time, but that generally doesn't happen because the body can usually take care of that by itself. If it can't, the pain will get increasingly worse until it's unbearable and the person goes to the doctor. Start chugging water and sports drinks like gatorade and powerade. Some juice is okay. For now, absolutely no soda, caffeine, energy drinks or alcohol. If you're properly hydrated, it helps the kidneys a lot by flushing out a lot of the bacteria.

Dehydration is the top risk factor for urinary tract and kidney infections. Even if it doesn't result in an infection, it will still cause kidney pain. The solution for this is also drinking a lot.