Ash, I'm just seeing this. I will have Nova in my prayers. If it feels hard it probably isn't a fatty growth but could very well be a sebaceous cyst. My RB Cody had one right in that area and it got pretty large as it filled with more fluid. It got almost to the size of a tennis ball and very hard. I had it checked of course and the vet explained it was a sebaceous cyst and we could drain it if it didn't do so on its own. It did finally drain and go down quite a bit. It seems to be under the skin like a cyst would be from your photos. If it is that it is painless and benign. I hope you get some reassuring answers at your visit tomorrow.