What Causes Recurring Soreness In Upper Abs Post Exercise?

My upper abs started being sore two days after doing an an workout. There was no pain for over a day after my workout, all I noticed was that my abs were a bit tighter than usual and not sore. 2 days after my workout some pain started to develop and worsen throughout the day. The only way to lessen the pain is by flexing my abs a bit. I had a no equipment football practice and during it the pain subsided but afterwards the pain returned. This is not a regular occurrence for me and I am an active teenage male. Any advice or help would be appreciated.