Your situation is pretty similar to mine. First learned to swim at 14 at the Y and then again in college, but was never great at it, especially the breathing.
I started again at 60+. I've been doing TI for about 2 years. I have to travel out of town to see my instructor, so I only see her about every 3-4 months. I still don't have the breathing down yet, but getting better. I train with a snorkel to get my form down, which someone else also suggested for you. It's great to get in the exercise and not worry about the breathing.
It appears you may have expectations that are too high and not achievable at this time, so you are frustrated and "fed up". Lower your goals to smaller steps that are achievable with practice in a couple of months. Then, move on to the next small step. Be patient. Find joy in what you can do.