[AlethiaSi]

my organization has fewer girls total than your pledge class did! BUT no matter what, after seeing so many pledge classes go through, there is ALWAYS an awkward time after initiation. It takes time to settle in and make friends, yes it can be cliquey, (especially with sucha large group) but the best way to do this is to be around, and make an effort to join conversations.
Also, like 33girl said, girls might feel uncomfortable asking about your illness or asking you to do things for fear of overextending yourself, especially if they don't know you or what illness you have.
I would definitely make an effort to talk to one girl a week, see which "groups" you seem to enjoy the most. They wanted you there for a reason, don't forget that!

Also, when girls join and then don't participate, it makes me very sad, because in a way, I don't get an opportunity to get to know them, Imean, maybe with such a large group there isn't the same mentality, but you may just make some really great friends. If you REALLY aren't feeling it after another semester, inactivity/alumni status is possible, disaffiliation is very extreme, but see how you feel after you give it some more time.