You don't mention your age or sex.
If you are a lady over the age of 45, or have a family history of ovarian cancer, then you may wish to speak to your gp to rule out any nasties. With the history you give, this is a very unlikely scenario.
Watch what happens to a sealed bread roll, or a plastic bottle of water when the aircraft ascends. That'll probably give you a better explanation as to what's going on inside, than any technical discussion of Boyle's law.
Talk to you pharmacist, colpermin, mebeverine, peppermint may help. Talk to your AME blah blah.