Serious swim issues!

I am trainig for my first triathlon and am having a lot of difficulty with the swimming. I used to swim a lot as a child, but many years ago. I'm finally starting to do ok on the breathing aspect, but my stroke is different almost every time and I am obliviously being very inefficient, because I can only go about 200 at a time without have to take a quick break. Any suggestions would be greatly appreciated! I still have 3 weeks before my triathlon but getting a bit worried!