Severe back pain 4 years after spinal fusion

I had a spinal fusion 2/2008 when i was 22 L5/S1 and almost a year after the surgery I was 95% pain free. I got pregnant with my 2nd child who was born 7/2011 almost instantly after i gave birth i knew something went wrong with my back and since then my back pain is literally getting worse by the day. I currently have severe lower back pain, hip pain and the entire back of my leg to my ankle is throbbing constantly. In the last 2 weeks i've started to feel this vibrating pain in my tailbone. I sat on the couch last night and i was looking for my phone bc i thought it was vibrating.
My dr. sent me to PT, i went for the 1st time yesterday. The physical therapist had me use the stim. for 10 minutes and a bunch of stretches. By the time i left the appt. i was bauling my eyes out. my ankle was and is hurting 10 times worse, it's starting to kill to physically pick up my leg when i walk and i feel like i broke my ankle.
The physical therapist said after 2 weeks of PT if its not helping he'll send me for pain management. My thing is how can you send someone to pain management without knowing what the problem is!
I'm going back to my GP again today in hope that he'll just send me to get an MRI or CT.
I had an x-ray in 12/2011 which showed the hardware was intact. like i said that was 12/2011 it's not MAY 2012.
Has anyone ever had anything like this? I'm trying to figure out the vibrating feeling in my tailbone. It feels like a tuning fork is on my tailbone everytime i sit or move a certain way. I've googled everything!! I'm starting to think that maybe a screw is loosening up and thats the vibrating feeling i'm getting?
i'm at the point where i'm sick of crying in pain,i have 2 kids to take care of. i'm in excruciating pain but it's to the point where i'll suck it up if they dont want to give me meds, i just want to know what is going on.

sorry that was really long i'm just so beyond frustrated