Minty, don't worry about which side you breath on and how often. We get told to breath bilaterally in the pool but that is less important in open water.
Sometimes it is beneficial to breathe on one side only. If the waves are coming from one direction then it is easier to breath facing them than with the back of your head to them. That way you can see whether there is water there before you open your mouth and won't be caught out with a wave breaking over your head.
Also if you are following a shore line then breathing to one side can help you to keep a straight line relative to the shore.
In a race, sometimes you might find someone swimming very close to you on one side, so it can be easier to breathe the oposite way, or you might prefer to breathe towards them so that you don't allow them to get too close.
I think the important thing is to be able to breath to both sides. Whether you swim bilateral all the time, or to one side only, swapping as the circumstances change is all down to personal preference.
I also find that I need to breathe more often in open water. I think the cold makes it harder to get air in and you tend to use air up quicker as you are working harder (body trying to use energy to keep warm as well as for the swimming).