A little frustrated today

So today was the start of a new swim session and Coach Michael is back from vacation - yeah! Unfortunately, while he was gone my form was left unchecked and I have this funky thing going with my pull. My right arm starts sinking too low when I breathe from the left side. This is because my left arm is already coming up to pull as I breathe when I should be holding it to my side, breathe, then pull. I'm a little frustrated because I had been practicing these past few weeks with the wrong technique and I don't know why Eric didn't notice it. Coach Michael had to look at me swim for a bit to figure out what was going on. But, on a positive note, Coach Michael said, "You've improved in 3 weeks. I don't know what you have been doing or if you have been doing anything."