I get painful bumps on my skin at least once a month, about a week or two before my period. They can be behind my ear, this month I have one on the bridge of my nose, near my eye, but they can be on the back of my neck or on my back, lower and/or upper, etc. They are not pimples, but they do dissappear after about a week or so. Sometimes it takes two weeks. What could they be?