First 5K, the wheels fell off, I mean my right shoulder

Did my first 5K open water swim today and I felt great until about 4K, where within a relatively short amount of time my right shoulder iritated me so much, I had to compensate by cycling through back/*** and then to free for the last 1000. It really hurt and completely screwed up my race. The thing is, if I have a "bad" shoulder it is my left, from throwing a baseball, yet it is the right that gave out. I breathe to my left only and the other thing I noticed is that I always have a tendency to turn right. Is this a sign of a stroke flaw? perhaps in the way I am catching and pulling? Does the opposite shoulder to breathing see more stress? If so, is this common? Is it common to veer in the direction away from your breathing side? Is the pull in the non breathing side stronger and that is why I am turning right? Alot of questions, but I need to fix it.