I had the exact same thing, it was seriously doing my head in!
But.. it's quite normal, you might be eating at such a deficit that your body is literally slowing your metabolism right down, or you're retaining fluid.
My Dietician last week told me on avg people lose between 4-7 kg (roughly double for lbs) between the first and 2nd months... I was despairing as I had only lost 5.1 kg... turns out, right in the middle!!
Try not to worry, it is happening!
I found upping my cals to 900 really helped!