A friend of mine went from a 34C to a 34DDD (can't remember if that is the actual size but its one size bigger than a double D.) all in a time limit of about 3 months so its fully possible.
I agree 100% with mamaofonetrying42. I'm 5 weeks too and I'm already falling out of my 34D's. I'm sorry it's so painful but you are doing what you should; just make sure to keep wearing a good supported bra. Good luck to you.
I have never heard of your bb being a sign of labor. Your bb get bigger at the end because they a starting to get ready for the milk to come in, but thats it. I would think that you have nothing to worry about. It just a sign of pregnancy. But if you are very worried about it go and see your doc, see if you can change your appointment. Good luck to you on the next 9 month :o)