HELP 2nd week blues

Hi all

I'm not all that new to MFP but just need advice.
Its my 2nd week back after giving birth to my beautiful baby 4 months ago. The first week back I had a great loss it surprised me of 2.9kg or 6.4 pound. This week I have worked hard but haven't lost any weight in fact I have put on weight. I'm am breastfeeding 2x a day rest she is on formula as my supply depleted to nothing last week.
I'm eating 1200 cals because if I eat more I put weight on and I also eat some of my burnt cals back but not all. Is there anything im doing wrong?