It probably has to do with the fall reirritating the area. It's still very soon after your surgery, so there's still some tenderness and everything hasn't set in yet (that takes about 6-8 weeks). It's good news that your nurse checked you and said everything looks good, but if you're still worried you can always have your doctor check as well. I had pain in the area about 8 months after my surgery and in that case my doctor said the battery did move a little bit, but it was nothing to be worried about and the pain went away in about a week or so. Hopefully you'll be feeling better soon