There are more now, but still only a handful of people who seriously work with adults with swim anxiety around. Literally, a smattering.
First place I’d look would be the conquerfear.com site and see if they have a certified or recommended coach nearby.
2nd thing would be a swim school. One of the places in a strip mall with a warm pool that specializes in kids swim lessons and that’s all they do. If they have adult classes try them.
3rd would be the total immersion video O2 in H2O you might find that one helpful.
I think after that I’d look for a generic learn to swim class.
As for what is going on, you have anxiety. You lift your head WAY up out of the water, either look at the ceiling or back to your feet when you breathe. You kick like a madman or madwoman in reaction to / in addition to / lifting your head all the extra kicking gives off a lot of CO2 which makes you feel like you urgently need to breathe. This in turns ups the anxiety, and in 25 yards you are out of breath and can’t imagine how you will ever swim more than 100 yards without stopping.
ID ing the problem is the easy part, fixing it is hard. Main thing you need to know at thie very moment is that what’s separating you from swimming say 400 yards at a time is all mental. It is not technique, there are people with the most jacked up technique ever who can swim for hours at a time, not fast mind you, but nearly forever. It a mental game right now. I think if you get the conquerfear video it will open your eyes. The book is good as well, but I think the nsippets of the basic drills she does on the video are better.