Someone explain the rules of poker to me.

[The once and future king]

Situation.
BB is 50.

I am under the gun. I have KK I raise to 150, small stack raises all in to 260. This gets 2 calls. When the action gets back to me all I can do is call the raise from the small stack.

Why the [censored] cant I reraise. I mean, I realy realy wanted to but cant.

I cant think of a logical game mechanic reason for not being able to, is it just a case of thems the rules boy suck it up or is there something Im missing?