The singer hopped on TikTok Tuesday to address all the speculation, which kicked into high gear after some paparazzi photos of her at her sister's wedding over the weekend were shopped to media outlets ... where she appeared to have some extra belly action going on.

Obviously, something like that is a little sensitive -- but some felt she definitely looked pregnant ... but now, Gaga herself is coming out to deny that, saying it just ain't true.

In a video she threw up, she's filming some makeup work she's doing on herself ... goofing around and having fun, but the news is in the superimposed caption -- which reads, "not pregnant - just down bad cryin at the gym." LG also encouraged people to vote in the same breath.

She added ... "register to vote at www.headcount.org." Of course, the fact she's not preggo is the headline -- 'cause, again, there was a bit of speculation over the past 24 hours she may be.

As you know ... Gaga is dating a guy named Michael Polansky, who's a philanthropist ... and with whom Gaga has been linked to for a few years now -- often looking head over heels.

He's not really in the spotlight the same way she is, but with all the pregnancy rumors swirling -- many thought we were going to see Gaga become a mom for the first time ... and that we'd be seeing a lot more of him. Unfortunately for her fans, not right now.

BTW, rumors about Gaga being pregnant have flown at this rate before ... her weight fluctuates sometimes -- and something like this happened way back in 2014 as well.