The advice by 'ed' is good. It might be worth explaining your predicament to someone more senior so that they can look out for you and get you more involved in projects - probably a mentor. It helped me a bit when I did it.
Growing up in one culture and working in another is a very difficult experience. Normal office jokes may not make sense to you and yours may not make sense to others. Make no mistakes about it, it is nobody's fault - just a natural difference in cultural/social background and would happen to anybody outside his/her natural domain.
But whatever you do, do not take the back sit. Get noticed by all means reasonable!