question for the lady runners...

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I just finished my first half marathon this past weekend, so needless to say the past few months i've been running quite a bit (about 20-25 miles per week).

I haven't been losing weight really since January (fluxuating up and down the same 3-5 pounds)... but i haven't gotten my period in over 2 months (and yes, i took a PT last month so it's not that...)

has anyone else experienced this? if i continue to skip is this worth seeing my dr about? i'm nto on BC either...i'm wondering if it's just from the increased activitiy level and am hoping it will work itself out but just wondering if anyone else has had this happen