Man I totally hear you! I have the same issue!! It sucks when my closet is full off all these nice dresses from a thinner year...
I have a bunch of dress pants for work that I bought in a size 10 that used to be on the large size but I got because it was comfortable and looked better when i tuck my shirts in.
NOW these pants fit pretty perfectly, and it's not cool!! I need to loose the weight because I refuse to buy any bigger pants and I know how silly I look when I wear clothes that are too small even though it may still fit lol. As for dressing your age, there lots of cute stuff you can still wear, just try shopping at a woman's store, not the same places you shopped at in college. There's lots of cute stuff that fits way better since it's made for women who are grown and have curves and don't want to show off their butt crack constantly!