We can't answer "what is it with me" here on a web site. You should look into counseling to help answer that, and maybe there's something in your past that makes you want to hunker down with just your family and not reach out. But it's good that your recognize how isolated you have become, and that you know it's not healthy.
If you are this intensely unable to socialize -- I would worry that returning to work, without first working on yourself, will create a huge and sudden stress: You will be expected to talk and relate to others all day, every day, starting on day one. If you have so far not been talking with or relating to others at all, can you see how going back to work would dump you instantly into constant relations with a ton of strangers all at once?
Please consider working on your social skills, and possibly getting some short-term counseling, before you even think about returning to an office environment. In an office or other workplace, you will be asked questions, and expected to respond knowledgeably and quickly; or you will be the one who needs to ask the questions, and if you hesitate about asking, your work will suffer quickly and your self-esteem -- which already sounds fragile -- will suffer, and fast. Don't use returning to work as a way to force yourself to socialize; that is not work's purpose and you may end up bitterly disappointed and just as isolated at the office as you are at home.
Also, look at your post: You say that you think socializing will "make me a better person" -- that is a big red flag that you currently think you need to BE a better person. Again, I think of counseling.
How old are your kids? If they are at least preschool age, why do you think you're not already doing anything to talk with or get to know parents of their classmates? Are they in any form of preschool or do you do "mother's day out" or playgroups or other things where you could meet other parents? That is a way that many of us, after having kids, get started on new friendships -- we have the kids in common at first, and over time, find friends with whom we have more in common. Even if your kids are too young for preschool, there are play groups sponsored by local churches or synagogues, community centers, or the "wellness" branches of local hospital chains. If your kids are school-aged, you need to encourage them to see friends too; take the initiative to schedule play dates (this will be hard for you at first but unless they are older kids, really only you can do this for them, so you have to pick up the phone and be ready for some "no" answers too).
You can seek out groups that match your interests but you will need a supportive husband or significant other who can watch the kids while you force yourself to get OUT of the house without kids or husband and be with strangers. Can you do that? Can you get online and find groups -- a book club at the local library just once a month? A cooking group through the community center? A workout class? What interests you? If you answer, "Nothing, really," then that's another sign that you need help regaining your self as an individual and an adult.
There may be other reasons you have "gone quiet" that aren't clear in your post, like trouble at home. And this all sounds like it could be a sign of depression -- isolating oneself is sometimes a big symptom. Please get a counselor or therapist; it won't be forever and it will jump-start you better than going to a job will. The job can come later, but if you use it now to try to force yourself to socialize -- the results could drive you deeper into isolation. If you can't afford therapy or counseling, check with your insurance; they may pay for more than you realize! Or go to your county or city health department, where the mental health division likely has sliding scale fees to match your needs; or try your local "women's center" where they can point you to free or low-cost help.
Do this for your kids if not for yourself!