Hey,
It sounds to me that you're making one mistake in your training program, and that is making a the 50m a psycological barrier by swimming the same discance over and over again. You will get very used to at what point it is time to surface, simply according to the length of the pool instead of listening to your body. And just as perow said, one day you might get a problem on a distance that's normaly okey, maybe on 40m. If you're not used to listen to your body's signals AND don't have a buddy, it will be a big problem!
I'm one of those without a buddy too, so I have to train 90% of my time alone, which means basically technic training... It is good to do repetitions so that you get comfortable with a distance, for instance 50m, but I also do shorter sprints or shorter lengths focusing on my head position or something. Normal swimming with restrictions of breathing (one breath every 5,7 or 9 stroke) also helps alot.
Do NOT do max attempt alone, it's as simple as that. When you get somebody to watch you, focus on your body, your legs, your mind, and challenge yourself. You will definatly make that turn!
Good luck on your training
Elisabeth
