Stuck with 20lbs to lose.....

I have been working out regularly for about 4 years now. I lost 50lbs within the first year that I started to change my ways. Over the last 3 years I have struggled going a little up and not so much down on the scale. I have about 20-25lbs left to lose to be at a healthy weight. I usually get so frustrated that I don't see results right away and wind up blowing it. I have done pretty well since the last week of January. I took a short vacation 3 weeks ago that resulted in a weight gain of 3lbs (which is what I had lost). So I have lost that and I am now where I was prior to the holidays, finally. I have went back and forth and can't seem to get these last 20lbs off. Its so frustrating!! I teach Zumba 2x a week and usually do the eliptical 3x a week with also 3x a week of weight training. I have noticied a little bit of difference. I just didn't have to do near the work when losing the 50lbs that I am doing now. I eat between 1200-1500 calories a day, usually closer to the 1200. Any advice to push through these plateau's?? thanks