I know it is easy for me to say cos not started refeeding, but don't panic, it can't be fat its got to be fluid. Carry on with refeed to the letter, drink as much water as you can and see how you go after your period has ended.
I discussed refeed with my pharmacist tonight and she basically said to me that refeed is a funny week and it isn't unusual to put on, but it will settle during maintenance, so don't be too down just yet x