Do not sign anything until you get professional advice specific to your situation.
Contact a nonprofit credit counseling or housing counseling agency that has certified housing counselors on staff as soon as possible. They should be able to assist you, perhaps by negotiating concessions from your lender. They will also examine your housing costs as they relate to your entire household budget and suggest a plan to get back on track. Credit counselors might also be able to alert you to government programs designed to help people keep from losing their homes. For more information, see www.nfcc.org.
It is also possible that you are in a predatory loan scam. When a lender keeps insisting on higher payments, this is a major red flag. You might also want to contact your state banking department or consumer affairs agency for information about your lender and advice about how to proceed.