American Slang – If Somebody Calls You ‘Hello Trouble’, What Does It Mean?

"I am confused" means "I do not understand."

From The Free Dictionary:

confused [kənˈfjuːzd] adj

1. feeling or exhibiting an inability to understand; bewildered; perplexed

"I am getting confused" has basically the same meaning; the implication is that they are in the progress of becoming confused ("I'm beginning to not understand").

A more common phrasing this (in my experience) is:

I'm starting to get confused.

This is a polite way of saying you've strayed into an area that they don't understand, and would like you to explain it differently or perhaps slow down. This also carries the implication that their confusion began recently; for example if you've been discussing something for an hour it's safe to assume that they're not confused about everything you've said, but that something you've said recently has confused them.

To address the source of your misunderstanding:

You mentioned that your guess as to what "I am getting confused" meant was "somebody thinks I am somebody else." If you actually want to say "somebody thinks I am somebody else", you would say:

I am often confused with Michael Jordan.

The with is very important; when you are confused with someone else, that means that very often people think you are that person. If this is something that has happened only once, not as a recurring pattern, you could say:

She confused me with [x].

Or if the event is still occurring, you could say:

I am being confused with [x].

Though this is unlikely, because usually if someone mistakes you for someone else, you clear the matter up immediately (that is, you'd tell the person they're wrong and the confusion would end before you would turn to someone else and tell them what's happening).

It's an idiom: to be for someone is to be on that person's side, to cheer for that person's success. It's opposite has the same structure: to be against somebody is to be opposed to that person, to hope that person fails.