plateau'd, confused, please help!

Thanks for having time to read this. I'm so discouraged.

I am 36, 5'6, and have plateau'd. Today I weigh 139lbs. I have extra fat around my midsection, which is why I know I have to lose more body fat. I am working on strength and core training because I would like to build muscle, be stronger, and have a flatter stomach.

My history: On March 26th, 2012, I weighed 150 lbs. I started eating 1,450 cals total, was going to the gym 3 nights a week to do the treadmill & bike, and lost 5 lbs. In May, I started eating at 1,200 cals total for 3 months (because I was on JM's 90BR meal -plan) and lost 9 lbs. before stalling out. I was exercising a half hour a day with JM BR and going to gym at least 2 nights a week for 2 hrs (bike, treadmill).

I was recently married (July 13). The week before, I'd completed BR and switched to 6wk 6pk & RI30. I also switched up to 1,500 cals total, then went on honeymoon/took a break hoping a change in diet & fitness was what I needed to break through this plateau. That was 2 weeks ago. I have lost nothing. I got down to 135 the week after coming back...and went right back up.

The only thing I can think of is that 1. My body is readjusting to eating more cals 2. 1,500 was still too low 3. I need more strength training.

I should add here that I don't have a HRM and guesstimate cals burned. I don't eat them back. I do try to eat as cleanly as possible. Today I upped my cals again from 1,500 to 1,754. Any insight into what the heck I am doing wrong and knowledgeable advice as to how to get myself re-oriented is deeply appreciated!