P90x

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Ok so i have done just two weeks of p90x im not wanting to get ripped out of it my partner is doing it an so am i im using it as my exercise i was just wodnering if any of u knew roughly how many cals would be a good average to use wen logging my exercise?? Also im worried that now im working out more ill need to eat more but MFP has put my cals dwn by 100 im struggling to keep within that an may weight loss is at a point where one week im u n the next im done i dnt seem to be going anywhere....... someone please hep im seriously losing motivation :(