So yesterday I went for a 30min jog for the first time in months. I also did about 30 sit ups afterward. Also, it just so happens that I'm supposed to be geting my period sometime this week. Last night I awoke from cramps that I believed to be menstrual. I took some Midol, drank a glass of water, and then went back to bed. This morning I go to the bathroom expecting to see red and there was none. I thought ok, maybe it will start flowing later in the morning and it didn't. It is now 2:22pm and still nothing. I am however still feeling a cramp here and there. I should also mention that these cramps feel exactly like menstrual cramps and that I've never felt cramping like this after a workout.

Am I cramping because I worked out yesterday for the first time in months?

or

Did working out shock my system to the point where its now taking a long time to menstrate?

no. if you haven't worked out in a long time you will get cramping/tension/pulling feelings in your muscles. stretch before you run, and stretch afterwards, and keep up with it and your body will adjust.

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Well I spent a day freaking out that I was pregnant because I spent the day with hideous intermittant period cramps, but NO blood at all. It was about 24 hours from first cramp to first blood. So I think sometimes they can be out of whack.