If you do not yet have a US passport or passport card that is valid until at least 6 months after your trip, you can use your birth certificate instead, either your original birth certificate, or a notarized copy of it. You can re-enter the U.S. with either a birth certificate or a passport.
A passport makes the entry a bit quicker, so if you can get one in time before your trip, that will be best. Here are some tips in how to get one fast:
An expedited service option, which takes 3-5 weeks to process your new passport, might be available, which costs $60 extra.
If your passport is still slow in arriving, call the National Passport Information Center at (877)487-2778 between 8am to 10pm, Eastern Time. You may need to call 50 times before someone answers the phone.
When someone answers, give them your passport tracking number, which can be found on travel.state.gov, and set up an appointment to meet with someone in person.
Bring to the appointment a second completed DW-11 form, a copy of your birth certificate, and proof of international travel, such as a letter like the one below, or a hotel confirmation, a flight ticket into Mexico, or an international driver's license.
This is one of their offices: Seattle Passport Agency Fifth and Yesler Building 300 5th Avenue Suite 600 Seattle, WA 98104