Exercise/weight gain

I have a question and hope you can help -- I am generally fit and in good health (by no means skinny).  I jog/walk daily.  I stick to a low carb (lean protein/vegetables) diet.  I am 30 yrs old, 5'7 and usually flex between 135-139 pounds.  I recently started an intense cardio kickboxing class which I LOVE.  I go 3-4 times per week.  Its an hour long class and it is super intense and works me out unbelievably.  Ive been going for about 5 weeks now.  My quesiton is -- why why why am I not only *not* losing weight.. but I've gained 3 pounds!  I did not join this class to lose weight specifically -- I joined for the natural endorphins from exercise -- but I certainly dont want to gian weight.. My diet has not changed.  The only difference is this class.  Im discouraged and don't know if I should quit the class .. But I do enjoy it.. so Im stuck.  Does you know why this could happen??   My mom keeps saying its because "your building muscle and mucle weighs more than fat" -- which I have heard a million times.. but its still really depressing..

[Renee Radenberg]

Your mother is right. You are building lean body muscle mass with that exercise and that weights more than fat so you have a 'weight' gain. Suggest using a tape measure and not your scale so you know you are decreasing inches. Your clothes will start to fit looser too.

[WenDDarling]

She is right... once you burn the fat and tone the muscle you apear (on the scale) to be gaining weight... but don't worry... as long as your not body building eventually you will tone the muscle that needs to be toned and then continue to lose weight till you are at the weight your body wants you to be.... GOOD JOB! I wish I had your motivation to excersize.... Kudos!

[refusingbondage]

THANKS FOR ANSWERING :)