I have difficulty breathing when I run?

First key, you NEED to relax. Running isn't that big of a deal. You need to breath in through your nose, then exhale from your mouth. Don't sprint in the beginning, and gradually get faster, at the end you should be sprinting and crossing the finish line. I find that holding my breathe underwater helps me build up lung capacity. Trust me, you're not going to be the only one finding it hard to run. Take longer strides too.