Are you taking measurements? If you're doing a significant amount of exercise, you may in fact be losing fat, but the weight of it is replaced by the weight of muscle. The surest way to determine if this is the case is to ask yourself if your clothes are looser, even if you're the same weight (or compare measurements).
If the exercise is new to you, what you might be seeing is temporary wait gain/stall due to the fluids your muscles hold while repairing themselves (which is an integral process to building muscle).
You say you may be lax in writing things down - start there, write everything down for awhile to see if you're fooling yourself into thinking you eat a certain amount when you really eat more.
Otherwise, I hear a lot about "psychological" blocks - maybe you get down to 150 and are subconsciously afraid to see a lower weight, so you may not realize it but you're eating more, making yourself gain the next week. To identify that kind of behavior you'd need to do a lot of self-searching. Have you ever been in the 140s before? Often we're afraid of seeing weights that are unfamiliar to us (so, um, ALL weights for me

). Other people report getting mental blocks when they get close to their goal like that - like, "diet" is all they know, how the heck are they going to manage maintenance? So they keep themselves (consciously or unconsciously) in "diet" mode by going up and down like that.
The other thing would be to check on how much you're eating - if you're eating too little (i.e., just your base points), your body may not want to lose anymore because it feels that's as small as it can safely get given the limited food resources around. (It thinks there are limited food resources, even if it's rather the case that you're just choosing not to eat.) If this is the case, try upping your points by a couple a day to see what happens there.
That's all I got for ya, good luck with it and CONGRATS on the awesome progress so far!!