I was born in Puerto Rico and my birth certificate has my dad's last name as my third name. My mom's last name as my last name, but all my documents are under my dad's last name. I am going on a cruise and my travel agent said that there is going to be a problem because my last name on my BC is suppose to be the same as my driver's license. Do I have to have my name changed legally or do I have to change some of my documents?

It would be far easier to merely change your name,

Did you just post this similar post under another name and discuss the incorrect name on birth certificate, on military record and on social security

No, it's that I have a first, middle, and two last names. My father's last name comes before my mother's last name on my BC. This happened because I was born in Puerto Rico. In Puerto Rico the father's last name is put first and then they put the mother's. For example if a Juan's father is Lopez and the mother is Ramos, the child born in PR will be Juan Lopez Ramos. When that same child comes to the US and gets a social security card his name is written as Juan Ramos Lopez.

Have you obtained a passport? You may not be able to disembark at certain ports without one. Once you have obtained a passport that will be the governing documentation.

Exactly, and when you file for a Passport you list ALL of the names you've used and the reasons AND you document anything where there's a question.

I don't see an issue. My birth certificate and drivers license have different names because I am married. In fact, my drivers license has my previous married name on it because I don't use my married name except for "social" events. I work and live under my previous name.