You are, likely, a U.S. citizen from birth. However, you have to prove it. In a large measure, the difficulty of establishing your citizenship depends on whether your parents were married at the time of our birth: if they were not legally married, demands of proof are much harder. Let me continue this answer on an assumption that your parents were legally married at the time of your birth. Do not disregard your Mexican birth certificate as a piece of evidence in your favor: if it states your father's paternity, it makes almost a half of your case (if your birth certificate does not name your father, you have a problem) You also need - proof of your father's U.S. citizenship, - marriage certificate of your parents; and - proof that your father resided in the U.S. for not less than 5 years before you were born (at least 2 years out of these 5 had to be after your father's 14th birthday). If you don't have these documents, they can be found in the archives of the municipalities where your father lived, where your parents got married, and in the national archives (for example, you can prove that your father lived in the U.S. for 5 years as required, if you obtain his tax returns and Social Security records for those years).
Answered on Jan 31st, 2014 at 10:02 AM