Help me understand NEW back pain

I'm hoping someone out there has some answers because I have really hit a wall as far as researching this...
I'm 29 years old and had my 4th back surgery 2 months ago.  This time it was an anterior fusion done through my stomach from L3 to S1.  A couple weeks after surgery I had xrays taken and was told the top implant had slightly subsided, meaning it had (in my own words) sunk into the vertebrae below and (their words) caused a slight fracture.  I was told it was fairly common and that we would just monitor it to make sure it didn't "sink" any further.  Just the following weekI had to move out of state and change doctors.  Obviously, my records came with me and the new doctor took a look at the xray on my first visit.  Unfortunately, he is a couple hours from my new home.  Less than a week after I saw him I started getting these intense pains in my back.  They are almost indescribeable.  It feels like a combination of boiling water and dry ice when it hits and then there is a clamping and twisting feeling that radiates.  The pains are ususally quick and quite often I can tell when they are coming (for example, I can no longer lay down because I know that if I want to move from a position while laying down it will be excrutiating).  Sometimes I get these pains out of nowhere when I take a step or shift.  At first I thought it was a muscle spasm and it very well may be.  But if it is it could go down in the book of records.  I have a very high tolerance for pain and I am on a bunch of meds so for me to feel it that intensely is...frightening.  My doctor blew me off, chalking it up to healing, making me feel like an over-anxious pest for my unwarrented concern.  Excuse the expression, but this isn't my first rodeo.  And we're not talking about a hangnail.  Something is wrong and I don't feel I can get anyone to listen and say anything other than "it's healing."  Has anyone had a similar situation with this pain after implants that have subsided?