I feel like I have no social life compared to my friends? Am I falling into a vicious cycle?

[Tina]

I have a lot of friends in school, on facebook, contacts on my phone and whatever. But out of all those friends, I really only hang out with 5 or maybe 6 of them. In the beginning of the school year I had plans like every weekend, each time with someone different. But ever since October or November, I feel like I have no social life anymore. My friends are all busy with their sports with other friends, family, or just other friends in general. Then I started to get in the cycle of comparing myself to them in every way possible. They have more friends than me (since they're more involved in programs/sports) and that they have a better life than I do. I'm on winter break now, and so far out of the two weeks I only have plans for like 6 of the days. I'm going to have a whole week of boredom and loneliness, and my brother doesn't come back for about another week and my friends are all going on a trip. I really don't like this feeling of loneliness, and I've been feeling like I'm a failure ever since I got my first C of the year on my recent AP Chem test (which I cant get over that, either). I'm starting to think that I'm messing everything up when hanging out with people, so that they don't want to hang out with me anymore and I'm starting to get a little nervous to continue with my plans for the week, afraid of "messing things up" leading to people avoid me. I feel like I'm being too paranoid, but recently I feel like I've drifted away from people. How do I get out of this negative thought cycle? I tried to keep my head up but there is always something that just brings me down again.
Before I used to be fine like this, home all the time. Actually, I used to LOVE it. But now, its just killing me and I feel ridiculously lonely because of it.
Also, I am home alone all the time from 9 am to 7 pm