green card questions

I need to renew my green card. I am 19 years old and new to the process. My green card expired last year. I need a new one as soon as possible as I am 7 months pregnant and have no health insurance and need to get a new social security card in order to apply for medicair, and in order to get a new social security card I need to get a new green card.
I sent off to get an I-90 form. I have questions on what to do with it after I finish filling it out. I can not afford the 260 filing AND biometric fee, and know that you can ask for a fee waiver for the filing fee. Do I send the request for the fee waiver with the biometric fee and my I-90 form off to the place in California? Or do I have to go to my nearest immigration center and do it there? And what if they do not accept my plea for the fee waiver, will they let me know and I will have to send in the rest of the money or will they require me to send it all again?
I really need some help. I've tried calling the number given to me, but all I got was automatic answering machines that provided no help at all.
If you can help me out, please email me as soon as possible. Thanks in advance.