Hi there, welcome to FitDay. My suggestion would be to start logging everything you eat if you haven't already. You might want to consider not making any changes to your eating the first few days, and something might jump out at you from your log/reports that you can identify as being a main contributor to weight gain. Sometimes getting it all there in black and white can show you something even if you think you're doing everything right. Good luck!
And now that you don't have to be perfect, you can be good.