Is my T-B3 Non-O visa a multi-entry visa while I plan my trip back to the States?

Is a T-B3 visa not for Laos?

There's no such thing as a multiple entry non-O visa anymore.

Are you actually on the 90 days of a Non-O visa, or are you on 1-year extension of stay?

I'm assuming you're on an extension of stay because you said you want to go back for "a few months" and a 90-day stay would not cover that period of time.

If you're on the 1-year extension of stay based on retirement, what you need is a re-entry permit. What is stamped on a visa is irrelevant because the visa is void as soon as you enter Thailand it's used up.

So check your passport and see if you can find your 1-year extension stamp, and if you can find a re-entry permit that's valid until the end of your extension. If you have that, then you are good to go. If you do not have it, then you need to purchase one from either your immigration office at the airport on your way out.