Listen to your question: "Am I going to have to go to the opposite extreme?"
Of course not.
Will you have to try harder to go against your nature and reach out and do some more stuff? Yup.
I'm the same as you and went through this transformation for the last several years. For all of my 20's and early 30's it was easy to be a hermit and lose myself in my work in NYC and still be "out and about a lot" and have work friends-and there was no FB, so it seemed fine. Once I moved to a new more rural location and quit work to have kids-WOAH. I had no friends except my handful of near and dears I'd had for 20 years. And I didn't really mind. But I started to get that bug like you when FB popped up and my few friends had billions of friends!!! There was a community around me of people who knew each other, and I was keeping on the sidelines.
LUCKILY I have one VERY social friend who blew into town about the same time as me and instantly knew EVERYONE. A testament to how gifted she is socially: I met her when she waited on my husband and my's table, and she struck up a conversation like nothing, and we saw her around and before you knew it-we knew her well. I dont' even remember how one thing led to another. She knows EVERYONE WELL. How does she do it? She reaches out. She invites people over, she has girls nights with co-workers, she jets off to meet up with old college friends out of state, she attends events-granted she has no kids and can do EVERYTHING. But still she invites me to do stuff all the time, makes my kids welcome, AND comes over to our house to visit us, and SHE makes it happen-I often don't think of it.
I decided to start doing a fraction of what she does and it's great, I have plenty of friends and interaction in the community for my style.
I started getting a sitter now and then and meeting people out. Not often, but it suits me fine to NEVER do that, so it was an effort. I attend gatherings when I'm invited even if I don't feel like it. I make it a point to approach people I dont' know and ask them questions at parties. I make it a point to call and email people to ask about them. I make eye contact and chat with regular neighborhood people working in the places I go. I got ballsy and had a PARTY and invited some new people I barely knew along with the few who regularly come over (and when I say regularly, I mena, like...twice a year). I FB a new person I've really met and spoken to after each new thing I attend. I don't gush on FB, but I comment occasionally and post occasionally, keeping it upbeat and not weird-I participate without overdoing it-when my nature would be to not even participate.
My social friend recently joined my gym, and we walked in together one day, and she "high fived" the guy at check in and cracked a joke with him (I've been going there for 6 ears and never said more than "hi") and in our Zumba class she knows half the class by name and is always chatting with everyone-again, I've been in that class for over a year and never talked to anyone! Now I'm more accessible and outgoing there just because she is.
It really is easy, it just never occurs to us hermits.
I still RARELY go out, and I still have a fraction of the FB friends many people do, but it' a huge improvement, and I'm right where I wanna be. Just always be sure to make people feel good about themselves and show genuine interest, and it's much more effective than just wanting them to like you. Your neighbor has got the social gift. People may not "miss you" when you go somewhere for three days (that's rare but would also happen for my friend), but people will like you if you like them and if you reach out more. Do it on a smaller scale. it feels good!