I know where you're coming from pledge.
My advice is to find out the root cause, in which there can be MANY!
Are you quiet? If you don't speak up you will definately will not be noticed.
Are you too talkative? You could be annoying everyone.
Are you showing any interested? They may think you aren't interested.
Are you showing too much interest? It can make you come off as being desperate.
Bad rep?
Guilty by association with a person that has a bad rep? Been there, done that.
Did you not go through formal rush? I didn't go through formal rush, and I had trouble getting the "feel" of things.
Is there something that sets you apart from the rest, even if it's positive?
Do you rub people the wrong way in general?
Did you piss someone off? Intentionally or unintentionally.
If you don't think it's too deep of a reason, I suggest you to stick around and don't give up.
People probably will eventually adjust to you within 8-12 months.
*EDITED* One thing i've noticed recently...people often ASSume that everyone knows what is going on. If you think that's the case, tell them you do not read minds!!!