I Am A 63 Yr Old Male With An "odd"

I am a 63 yr old male with an "odd" pain that occurs frequently from my right waist line/kidney area that spreads down most of my buttock. I was treated for a kidney infection and my doctor suggested I needed an MRI but I have no current insurance. I've had thee symptoms for two months. My Dr. did not hazard a guess what might be causing this pain as it comes & goes. Sometimes when it strikes it's like a severe spasm & comes without warning & I can hardly move...any ideas?