If it helps, when I was re-learning how to swim as training for Anaconda I found struggling to breathe meant I was pushing too hard - especially if you haven't done significant swimming for a while. Slow it down and concentrate on being smooth through the water, and as your fitness comes up you'll find breathing (and effort, and speed) a lot easier.
I was doing about your pace (26-28min/km) when I started, and got my biggest improvements from technique rather than fitness/power.
Thanks. I know I was going too hard, I will just have to work on it gradually. I have never really swum laps before, except when I was learning as a kid, so a big learning process. Pace is approx, I didn't really look at the time, maybe a it slower than that.
Yep, I was the same - once I finished school swimming I didn't do anything until my early 30s and then started wondering how I was going to survive 2km in the ocean. :)
Pretty sure I couldn't survive swimming 2km in the ocean!
Wetsuit helps a lot. Constantly cramping legs doesn't. :)