It’s normal to come down somewhat after coming back from sem, once out of that vacuum, it’s almost impossible to maintain the levels obtained while there. What’s important is to keep looking forward and up. Life is a downhill escalator. If you’re not working all the time, you’re going down. The more you work, the more you will climb.
As to the question of who you are, you are whoever you want to be – not the girl before sem and not the girl at sem, but a combination. You know what it was like to struggle like you did before sem and now you have goals that you were able to set your sights on while at sem. Let go of the image that you have of yourself before sem and just keep moving forward. It’s the yetzer hara that’s telling you that you didn’t really change and that you’ll never change and can never be like you were when you were in sem. Don’t listen.
Try to get some basic values/guidelines set up for yourself before you go looking for shidduchim. You can’t fit yourself into the mold a boy might create for you. You have to define yourself more and then you’ll know when there is a good fit with the boy you meet.
Like others have said above, get real life guidance. There are many continuation programs in US for after sem. You could find something that interests you and go to some classes and see if the teachers there would be good sources of advice. Don’t rush. Good advice is not easy to come by.
Chin up and hatzlacha rabba!!!