My advice to you is this,
If you are pretty small for a female,
You might not fit into small for men (I'm a medium in female sizes, and I wear small in men's)
However, if you don't fit into those, then you might have to think about Large in youth sizes.
Also, A lesson that I learned the hard way;
If you're tight on money (Like me)
Then it's a good idea to go to a thrift store for your first trip.
I got so excited that I ended up going broke and having to borrow money until my next paycheck xD
That way, you can buy tons, not spend a lot, and experiment with lots of different looks.