I have been traveling to mexico every 5 months and i used to get thru the border was my birth certifiket.?

WHAT DO I NEED TO GET A PASSAPORT AND WHERE CAN I GET A PASSAPORT?

you can apply for a Passport at your county courthouse

Courthouse, post office. You don't need a passport unless you're flying.

you don't need a passport to go in to mexico you just need your i.d.

You can get them at most post offices. Sometimes you need to make an appointment, other times you can walk in. Most post office even take your picture, which is required. Along with birth certificate, marriage certificate (if you are female), and picture ID, and I think it cost $80. It takes about 8 weeks to receive it, but for more money you can expedite it.