I recently started doing xtra squats because I want the thicc, for reasons

So I did some squats according to advice on the internet (check for butt wink, activate glutes first, intra-abdominal pressure), like 3 sets of 12, but then I almost passed out (not an exaggeration) from either a lack of oxygen from holding my breath every rep to maintain the pressure, or just using muscles in my lower body ive never targeted before.

Is it normal to come close to passing out every rep in the 3rd set or should I be doing something differently?

Also anyone who has the thicc feel free to tell how to get the thicc plz