Your last many months have not been especially pleasant. You've spent a lot of time feeling sick, having no energy, wondering when you will feel well again. You've persevered through it all and managed to keep up in school for the most part. Even if the report card doesn't say so you've got straight A's for effort alone in my book. I know the effort required to get through school depletes most of your energy. You've missed out on a lot of socializing simply because of how rotten you feel so frequently. For an out-going girl like you that's a hard thing, especially for your senior year.
To add insult to injury you've had a couple of long-time friends turn their backs on you. They've been people to whom you've given yourself repeatedly when they had times of trial in their lives. You've listened and consoled when they needed it. Sadly, they have chosen not to reciprocate in your time of trial. While that's disappointing enough the insensitivity toward you and downright ugliness has been the bitterest of pills. I know it's painful for you. It's been painful for me to watch. Unfortunately, this is how life is sometimes. It's not always fair and people can disappoint.
After you've dried the tears it's time to move on. If someone is consistently cruel at a time when your greatest need is kindness and they ultimately tell you they don't want to be around you, you're better off without them. Truly. Let them go. It's making room in your life for people who are kinder and more faithful. You haven't lost anything of value because in reality you didn't have it to begin with. The difficult circumstances in life merely revealed true character and the quality (or lack thereof) of a relationship.
Likewise, this time in your life is revealing your character and the character of others. Just as the fair weather friends are flying away on the gusts of wind, the true ones (few though they may be) are showing how deep their roots are and how immovable their affection and concern are. Those are the relationships to nurture. Those are the friends to treasure. Hold them close in your heart and let it make you glad rather than holding the pain caused by false friends. Count yourself blessed to know the friends who remain are proved true.