Depending on where you go to (and what type of institution) a bachelor's alone is sufficient. The more exclusive places might require a teaching certificate, but those are easy to get and, in any case, such requirements tend to be quickly relaxed when talking about harder to fill positions, like calculus teachers. You might find you enjoy this. If you don't, it can give you the foundation to find something else you might enjoy. Many companies are also constantly looking for skilled native workers. I've friends working in everything from web design to rehab counciling.
I'm not very happy with the current state of the US to say the least, but being born American and simply natively speaking this language is just an unbelievably valuable gift that one should never take for granted. It's really a gateway to the world, even if it's one hell of a scary gateway to step through the first time.