This is Dr. David
thanks for requesting me.
old brown discharge can be from some of the uterine lining which didn't come out completely during your period
you could be ovulating around this time
hormone changes can cause breast tenderness.
I bet your next period will be more regular
hard exercise, running can cause your periods to be shorter than usual
keep up the running and exercise as this is good for you.
let me know if you have other questions.
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