Help! extreme pain in back and right side

So this past super bowl Sunday my boyfriend took me to the emergency room because I was having excruciating back pain. It was in the middle of my back but only on the right side of my spine. I was tested for all infections and even had a sonogram done to check for kidney stones/gallbladder attack etc. but it all came up negative (thank God). They sent me home with no meds and said it could just be a "pinched nerve" and to take Tylenol. So the next day the pain was unbearable I could barely walk without crying and screaming...I went to go see my regular OBGYN and he suggested it might be a kidney infection. So now I am on medication for a kidney infection and also have a prescription for Tylenol...I noticed that the pain started to subside but just tonight about (3 days later) the back pain is back again. What is going on?! Is it just my skin stretching to make room for the baby?? I can barely sleep because the pain is keeping me up...ugh. So now I'm up at 2:35am eating cereal don't know what to do...help! Has anyone else felt this type of burning back pain only on one side or am I going crazy?!