You’re tired. Your brain has apparently decided that remembering why you walked into a room is optional. Your jeans feel a little tighter, your sleep isn’t what it used to be, and some days your patience seems to have disappeared completely. So…is it stress? Your thyroid? Perimenopause? Welcome to one of the great health mysteries of your 40s! The frustrating answer is that these three can look surprisingly similar—and sometimes more than one may be contributing at the same t