Sounds like you're not incorporated--if you were, then you would have been required to do bylaws by the state. You don't have to incorporate, but it's a good idea from a liability standpoint. There are things called "unincorporated associations," but even if you are one of those, you should still have bylaws, although no one will make you have them.
You should have bylaws so you have something to fall back on just in terms of basic things like officer elections, terms, etc. For a sample set of bylaws in compliance with Virginia law, go here:
www.nonprofitlaw.com/bylaws.doc.
Grab a copy of your PTA bylaws and modify these PTO bylaws as applicable for the stuff you were doing before as a PTA (in terms of officer terms, election procedures, stuff like that). You can also dig around that site for some great information about filing for incorporation and tax-exempt status (see here:
www.nonprofitlaw.com/taxworkbook.shtml).
