From what I understand about expanders (I'm on my 3rd set) they are put in "folded" and when your doctor fills them with saline then they open all the way up. I totally understand your discomfort - my left side is low and near my underarm. It pushes against my rib and drives me nuts. Other than going in and moving it, there's not much your doctor can do about it. Likely he will tell you to rub it up or down or in or out so that it moves to the correct place - and I know from personal experience that it is easier said than done. I've been trying to get mine to shift for the last 5 months and they haven't budged.
Talk to your doctor about it and let him know what's going on. You shouldn't be in pain, so maybe he can help. He'll also tell you what you can do to try to help and you'll be able to discusspockets to prevent something like this from happening again.
Good luck!
Angi