BR
Registered
As a recently certified diver, let me just add that a few months before we did our OW class, my boyfriend was phobic about water. The first time we went to the pool, he could only do one lap. But in just a few short practice sessions, he could easily do the required swim and more. It may not be so much that you are physically tired, but just need to get comfortable in the water and learn to breathe properly. If you can get air efficiently, you can swim a lot further. Just a thought.