Don't get rid of your old clothes!
That's my most important piece of advice. Wait a bit. You may well lose weight, it happens. I lost masses after ds (though, sadly, not after dd!), though it came off after a year, by which time I had sent many of my pre-baby clothes into the world to seek their fortunes in various charity shops.
Also, part of what you may be feeling now may be the well-known "post-baby-loss-of -mojo", which is connected to this sudden sense of "who am I?" , "how are mother supposed to dress?". That's a weird thing, but it, too, passes. And you are only 25.
I'm (a lot) older than you, and would, rahter boringly, suggest that Gap is good for cheapish, acceptable, smart-ish work clothes.
After that, well, you have to re-connect with who you are, and how you like to dress, and then buy clothes, from all over the place, that match/express that. It's weird at first, but it does come back.
I'm a plump, middle-aged person, and basically try on lots of clothes, whenever I get a chance (which is, as I'm sure you know) not that often, and buy things (anything) that looks vaguely flattering. so I suppose I would suggest trying to go on a window-shopping trip, some time when your child will snooze through the experience. Don't buy, just try, and get an idea of what looks nice.
And someone on here once passed on the tip: wear make-up, so that you don't look utterly sleep-deprived in the fitting-room mirrors. Always takes the shine of the loveliest outfit when you look at your face and think "Blimey! I need rest. What am I doing here?"
And congratulations on your dd.