Why do I always feel bloated? I'm the opposite of constipated so I don't know what's wrong? I also missed my period for the second month!

? pregnant. I hope you have done the obvious, checked to make sure you are not pregnant. Also, lactose intolerance and celiac disease are 2 underdiagnosed reasons for your symptoms similar to yours.Get checked.
IBS. Assuming the opposite of constipated means the stools are loose, or worse, then likely irritable bowel syndrome. Start off with stopping all caffiene, and limiting carbonated beverages. See if any association with fatty foods, if so curtail these as well. Could be a gallbladder issue or a bowel disease so if symptoms persist after the above get it checked out. Also if blood is involved.