Tidbit of info about me

Hi I've been using MFP for awhile but just recently started utilizing peers (mess brd) for support. I decided in Nov 2009 that I was ready to get my body back so I started working out (cardio) I own a treadmill so I started walking daily until I could run for a 30 min run. I have gotten faster and added a gym membership. In November I started at 139 pounds. I am 5'3". I've had three children, my youngest is 3. It took like 6 months before I saw any budge on the scale and I actually felt like the incredible hulk. I was retaining sooo much water. I just stuck with it because in my mind physiologically it was impossible that I wouldn't at least tone up and lose some inches. So I kept with it. Then in July 2010 I dropped 20 pounds BAM! It was crazy! My co-workers were gossiping like crazy!! So in September 2010 I was at my lowest weight of 114 and felt AWESOME!!! I decided to start MFP calorie counter to maintain. To my surprise in January 2011 I started gaining weight and I keep gaining!!!! I have no idea why. I eat right around 1200 cal give or take either way some days, I'm not a junk food junkie at all and I don't drink anything but water (occ crystal light) and skim milk. I'm working out 5-7 days per week, 90-120 mins of cardio and light weights lots of reps for toning. And recently it seems like I'm retaining TONS of water. My skin is tight, my weight is up more and I can see it in my skin appearance. I cant figure out what the heck is going on. I'm researching for answers and remedies and I'm thinking about starting up a HIIT routine. I just wonder has anyone else hit a plateau this far into it or gained weight this far into it???