Not to worry, we have actually tackled this issue before.
This could be something you are eating or drinking prior to heading out, or it could be something medical. Try keeping a log of what you consume before running, even up to 3-4 hours ahead. Also in that log keep track of time of day, type of running, distance, and even temperature.
You may need to discuss this with your doctor. But do the log first to see if you can detect any patterns (when it's worse for example). If you do go to your doctor, you will be better prepared.
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