In college I dressed for class. Skirts, nice pants, cute tops, fitted sweaters, any combination of these items really; I put effort into my daily dressing routine.
My secret was that the days I dressed up were actually the ones I was feeling down. Whether I was hungover, or tired, or sad, rather than wearing PJ's to class I took a deep breath and sucked it up as I sucked myself into stockings and an outfit and I was on my way to a better mood.
My standard issue Loyola hoodie was relegated to the apartment and late-night adventures to other peoples' apartments because I believe that any bad mood could only be made worse by a bad outfit.
A good outfit on the other hand makes you look good, when you look good other people notice, and when other people notice you it boosts your self esteem and, hey, look at that, you're feeling better already.
My point is, if you're feeling dumpy, don't dress frumpy (I couldn't resist the rhyming, that makes me happy too)! Dress up and you won't feel down anymore. It's as simple as a white favorite tee.