Tessica's manager, Gina Rodriguez, tells TMZ ... Tessica and her fiancé, Dewitt Madison, are expecting their first child together. What's more ... they're going to blend their family. She has 5 kids from a previous relationship and he has 4 kids. Yup ... 10 kids together!!!

We're told they've been together for a year now -- and got engaged last June -- but dated many years ago. Btw, he owns his own lawn care and floor cleaning business.

Tessica -- better known to her legion of fans as the Gorilla Glue Woman -- doesn't know how far along she is ... but has an appointment next week for an ultrasound. For now, the proof's in the puddin' ... she's got not one, not two, not three but FOUR positive pregnancy tests. And, yes, the nausea's here ... and it's real.

And, for those who are wondering ... yes, Tessica's hoping the Gorilla Glue incident doesn't affect the baby whatsoever. #CrossingFingers.

We're told she had taken a pregnancy test right before her mommy makeover last month ... and it was negative. As we reported ... things went smooth after Bev Hills plastic surgeon Dr. Michael Obeng worked his magic ... but she got some scary news after the same doc -- working on a boob job -- discovered lumps in her breasts.