yes bf expert can tell you. it's not how wide open the mouth is, it's the action of the tongue that matters.
they can all yawn!
the movement of the tongue pushes the breast to the roof oh the mouth thus squashing out the milk. if the tongue is tied down the baby can't stick her tongue or so can't scoop the breast so to speak.
the tip of the tongue is a clue as well, think of a heart shape, but not the pointy end but the 2 "bumps" - the tongue will be the same, as the pointy bit is sort of pulled under, tied down.
you can possibly see a thin membrane/skin like a sail under the tongue connecting it to the base, that's very typical and my DS5 had that.
but my DD had an atypical tongue-tie which was a thick chunky piece of skin at the base of the tongue literally shortening the tongue.
both midwife and health visitor were unsure, but I just knew something wasn't right.
she actually also had a problem with her soft palate too, so latching on was a nightmare! I was bf her, but tried a bottle in desperation to make it easier for her, but she struggled even more and just kept on releasing the latch, it was just too much hard work.
the roof of her mouth was too domed/arched, so no matter how much she was trying she could just never press the boob (or teat) enough.
think of a pair of pliers when no matter how hard you squeeze the handles the tips just won't grip.
My osteopath, who realized this problem, manipulated the cranial plates, which in turn effected the soft palate and flattened it out, so the latch improved massively.
we had 2 sessions 3 weeks apart, sorted.
you might want to get a cranial osteopathy session to check for this or any other problems that could prevent a proper latch.
let us know how you are progressing, I hope you get the help you need asap!