The Dreaded Plateau

How tall are you and what's your current weight? How long have you been dieting and do you ever take breaks? Is the 1,300-1,500 calories your "net" calories or total? Do you use a food scale? Do you eat out often? Do you log every single thing you eat? Do you do weight training (I hope you do considering you work with a trainer 5X a week)? Generally, in order of common-ness, "true" plateaus are the result of:

1) Underestimating calorie intake. Many people do not weigh their food but still think they are estimating calories correctly. They're not (even if you're using measuring cups, there can be underestimation). Some people don't log on some days but still claim they are not eating that much on their days off. But they generally are. Restaurants can also screw you up since the calorie counts are inaccurate. This is why I often leave ~1/4 of the dish on the plate and but log the entire portion. Alternatively, you can eat the whole thing and log 1 1/4 portion.

2) Overestimating calories burned. MFP estimates are exaggerations. Even HRMs may be off. If you "eat back exercise calories," try eating no more than 3/4 back. Since you're probably used to the dance lessons, I doubt you burn that much there. But your personal trainer should be kicking your butt in each workout. Otherwise, you should reconsider employing him/her.

3) Overstressing your body with too much cardio and too big of a caloric deficit. This can do strange things to your hormones. You could cut back on cardio while doing weight training 2-3 X per week and see how that goes.

4) Dieting too long without a break. This is a problem in particular for those close to their goal weight, and those with lower levels of body fat. Again, dieting stresses your body and messes with your hormones. If you have the first 2 points in check, you may try taking a break for a couple weeks and then starting the diet again. You generally want to take some time off from much exercise during this time as well.

5) Thyroid or other health issues.

If you don't already, you should start some weight training. Also, eat enough protein: 1-1.5 grams per lb of LBM.

Sounds like you need a diet break. Try eating maintenance calories for a week or two to recharge your hormones (leptin, grehlin, thyroid) and give your CNS a break.