I do find at the start of a session breathing is awkward and i always feel out breath, but by the end it does feel much more natural and less of a problem, even when swimming harder. The real issue comes when trying to concentrate on some technique then i end up forgetting about something else. E.g. last week I was trying to push my arm further forwards but kept screwing up my breathing.Sometimes I even forget to kick properly I am so focused on trying to improve the catch/pull.