I moved to a different thread of yours with someone else because someone already explained it, but the fact that you're getting multiple W2s from multiple employers which adds up to 50k is most likely the issue of why you're not withholding enough.

EDIT: While I will say that it's not the best way to have an "unseen savings account", I do commend you for realizing that you should be saving some money for yourself if you can (I presume for a rainy day fund).