Some input from a newbie, if you will accept it
One obvious thing I noticed was your frequency of turning for a breath increased as the video progressed. You started out with every three or so strokes, then you end up breathing every right arm stroke on the return lap. This makes me believe your fatigue/need for air begins with not getting enough air from the start of your workout. Possibly start your workout with breathing bilaterally; or if you cannot do bilateral yet, get a breath every right stroke. I only mention this because I found that a consistent breathing pattern right from the start helped me minimize fatigue.