IIFYM - Weight Loss Plateau?

MikeCopa

Hey people,
not quite sure where to post this but I've got a rather urgent question because this drives me nuts. So I began with If It Fits Your Macros about 90 days ago and at first everything went just fine. Right now however, I'm somewhat stuck (at least it feels like it).

I'm 18 years old by the way and started out at roughly 135lbs on day one. My TDEE should be near 2500 cals, therefore I reduced my calorie intake by 500. I also go to the gym 3 to 4 times a week. Initially everything worked as expected, I steadily lost a little under 1 pound per week, just like I wanted. After a little fluctuation throughout the days I weighed about 127lbs on day 70.
As christmas came nearer and nearer I started to eat about 2500 cals for an entire week with two cheat days on 3000 cals, should have been a surplus of 1000 cals in total, right? Right after New Year's Eve however I was a good one and a half pounds heavier than before and although I've been in a deficit again for two weeks by now the weight just doesn't want to drop. Technically the 2000 cals I had been consuming before and I'm consuming these days should still guarantee a steady weight loss, shouldn't they?

EDIT: So my question is, is it a good idea to slightly drop the calories to let's say 1800 and add a little bit of cardio to the mix or did I somehow damage my metabolism over the course of the last couple of weeks?