Since you have already had your tubes tied and added to that you are on pills and this means that your chances of conception are almost nil. It is likely that you are suffering from an infection of the urinary system
along with some gastritis
. Please get investigated for urinary problems and see a physician to get treatment for the gaseous distension. As you missed a period, go for a blood test
and a sonogram and see your gynecologist for further support. Good luck.