Sad all the time

Hi, Ladies. Having a bit of an issue here. I have a wonderful life...awesome marriage, healthy kids, food on the table, etc. But lately I've been having inexplicable, overwhelming bouts of sadness. It comes out of nowhere, and when it hits, I'm literally on the verge of tears, sometimes for days at a time. I don't want to go anywhere or do anything. I get really angry with people for no good reason. It'll hit me for a day or two, then disappear. I've also been having issues with painful cramping and heavier periods. I'm not pregnant. What's wrong with me? Thanks for listening.