there are tons of things that can affect weight loss...
water retention is one....too much sodium, not drinking enough, TOM can all add to water retention
muscle building...if you have been doing weights as well as cardio it's likely you could have lost fat, but gained muscle...so while you're losing it, the scales don't register it....they say muscle weighs more than fat...not true...but if you have 5lb of muscle and 5lb of fat...the muscle is much denser than fat so takes up less space...so check your measurements!
hth