I have already posted on this one, but I have more to say.
1) Do not feel hurt that sororities released you because of grades. Usually, they have no choice even if you are a really sweet girl
2) The fact that your grades aren't high enough doesn't mean that the sororities CAN'T give you a bid IF they get special permission from their national. Of course this all depends on lots of things including the rules of your school, whether or not the sororities' nationals are flexible, if they could get other people with better GPA's and lastly, how far away your GPA was from being acceptable (a 1.5 when you need a 2.5 would be bad news, but a 2.4 might be negotiable depending on their situation).
3) Maybe they LOVE you and they can't wait until you get your grades up so that they can have a chance for you to pledge later!
I hope this helps