Does L4 Fusion Of The Sacrum Cause Lingering Pain?

I had a lumber fusion of the l4 to the sacrum just six weeks ago and as soon as I get up or try to walk around I still have alot of pain. I wear the brace on going out which isn't alot as this is painful. At this stage should I still be in a lot of pain, it also gets painful to lay on my back if I have been standng up for a few minutes....I am desperate and a little concerned as it really is painful..Please help me