I feel like I've fallen into this too. There's so much else going on - I'm tired, don't like to get up early, take minimal time to get ready for work.... I do still dress nice for work but just can't be bothered much with makeup.
I just wish I could be one of those people who could do myself up everyday. It feels like so much commitment.
My suggestion for you is to plan nice things now and again for yourself that require you to look nice, which will help you feel better about yourself. What about cocktails with the girls some night?