Unable to walk very far after spinal fusion

I had a spinal fusion L1-L5 4 months ago.  Although I have had an improvement in the back pain, I am having problems standing and walking for very long.  After about 5 mins I get a deep ache and tightening in my back and pelvis.  I am under the physio and doing core strengthening exercises at the moment.  Has anyone else experience this type of ache/pain which has immobilised them after a fusion and did it resolve after a while? 

I had L3-S1 done over 2 years ago.  Wore my back brace religiously.  Finished PT with great movement and strength (but then I'm a rehab freak and take it very seriously almost to the point of excess).  Avoided ALL prohibited movements (lifting, twisting, bending) because the brace wouldn't let me.  By 6 months, it was like the surgery never happened...well...except I have a tough time tying my shoes...and I can't touch my toes.  But at 69, who the heck cares...

So...  At 4 months, you still have a way to go with PT and strengthening.  WEAR THE BRACE!!!!  It's a HUGE help.  If you're doing any no-nos that can aggravate the back...STOP.  Also, note that a fusion screws around with your nerve roots so expect nerve pain for a while.

Remember that a fusion is the meshing of your hardware and any bone grafts with your original "equipment".  This takes a long time...like a year...and the improvement is very, very gradual.  Give it time. 

 I am 4 monts out of L3 4 5 fusion and still have problems walking more than  a mile. I have right lower extremity radiculapathy sometimes pretty bad.  I've not experienced muscle tightening.