I am unsure who to turn to with our home settling problem. The house is 22 yrs.old and we have lived here for 6 yrs. A couple of months ago we noticed we could no longer use the dead bolt on our back door. Now we have to use a lot of muscle to lift the door when we want to close it. We live in Magna, Utah (Salt Lake County). Who do we call to investigate this problem before it get's worse?

Is it a wood door? Im guessing that it is,
Wood doors will move all year long and it is normal for them to swell and stick. Especially when its humid for a while.
Tell me this. As you look at your door from the inside,
Look at the gap at the top of the door is it greater on one side than the other? If it is then the floor has settled, and you may need to jack the floor up to truly fix this.
Or call a carpenter to do this for you.
Another fix is something you can do yourself. Open the door and engage the dead bolt, close the door as much as you can and with a pencil make 2 marks atop the and bottom of the deadbolt striker(or bolt). What this will do is show you where the striker is in relation to the keeper,(what the striker goes into to lock the door)
You may notice the keeper is high or low, just adjust the keeper to line back up with the striker or bolt. Tools you'll need for this would be a utility knife, phillips head or flat head screw driver, hammer and chisel, and possibly a drill and a 1" bit, just incase you have to rebore a hole. i dont think in your case youll have to do this, most likely youll just need to drop the keeper down maybe a 1/4". Good luck