First, accept that you were never as much of an extrovert as you once thought you were. Realize that you are energized by the time you spend alone and give your batteries enough time to recharge before going back out. Teach yourself that there is nothing wrong with spending so much time alone and that, in the long run, you're a better person for it.
Remember that for years you've wanted more time to spend on creative endeavors. That time is now being provided to you. Use it wisely.
Start a one woman campaign to learn to love yourself because you might as well enjoy the person you'll be spending so much time with.
Indulge in self-reflection. Start a conversation with yourself and listen to what you have to say. Begin to dig out the truths that you've always hidden and allow them to see the light of day. Spending so much time with other people has allowed you to hide too much for too long, and you're beginning to hunch under the weight of all those lies. Lose that weight.
Stop turning to food to fill the void that you created.
It's okay to weave a cocoon and incubate for a while, as long as you finally emerge as a better person. Instead of getting caught up in the fear of being alone, take the time to grow your wings. Invest in yourself, love yourself, learn as much as you can and eventually you will be ready to come out again.