First figure out if you really are an INTP since you're unsure. From your post I get the small impression you're something else, but you need to get a good handle on that. Second, if you really are one, psych would be a bad choice. The Drenth books get into this; he has a PhD in psychology. It's a 1-1 profession largely which is horrible for INTP's.
but I just LOVED the idea of being able to help others
An INTP might be attracted to the idea in an Fe inferior kind of way, but that kind of desire doesn't ring the right bells. Try being a F dominant with a T inferior for size, which is perhaps why you typed as an INTP.