Ashley-
I truly feel for you sweetie. I have people, even family members, who just don't understand. And many of us say this over and over, but I'll say it again, here goes...
People who don't live with long term, daily, chronic pain do not understand at all. They can't begin to imagine how much pain we function with on a daily basis. They don't realize that we have "adapted" if you will, to living with constant pain, therefore we have basically forced ourselves to act as if things are ok...we smile and laugh, we spend time with family, we go to work, we just function because we have to. We have become used to "hiding" most of the pain mostly because we don't want people making the comments that are made to us and behind our backs. I mean, just because we don't complain, doesn't mean we don't hurt.
I don't know what the answer to fixing this problem is other than having those people who make such comments live for one day with our pain so they might better understand, but we all know that isn't possible. I do know that the pain we feel on a daily basis would make most people climb the walls!
You are an adult, and regarless of what others say or think, you have to do what is right for you. If they can't understand that, or aren't willing to at least try and be more understanding of it, then they should just keep their comments to themselves- period. Don't speak of something you know nothing about.
If they ask, do as DJ suggested and simply tell them you don't wish to discuss the matter. If they get upset about that, it's their problem. Sometimes you are darned if you do, and darned if you don't.
Please take care and try and enjoy your holidays sweetie. We are all here to help support you.