Hi Amy!
Freelancing is definitely the way to go. It might take a while to find clients, and it can get a bit lonely working from home all the time, but I personally prefer working for myself. I can work at 3 a.m. in my pajamas while eating ice cream if I feel like it. (grin)
You can either keep working for portrait studios, or look for photographers who do model/actor/corporate headshots. That's a good next step up. Cold emailing and great samples are the key - be able to write a polite introductory email with a link to a before/after gallery....and then send the email to photographers/studios you find online....at some point you'll hit pay dirt. =)
FTP, Paypal, and websites like
http://www.sendthisfile.com are good friends of mine.
Good luck!