Hard to say, but my best guess is that you had water retention leading up to your period, and then let go of that water. IF is still a good option and your weight should still trend downward over time :)
the week before our period is our heaviest then the week of and week following we shed. that mid week lowest then repeat the shit show 🤣. also maybe your bad was less carbs. it takes 2.2 lbs of water weight to process a full serving of carbs. my “bad” is a tillamook teriyaki meat stick to not impact the balance too bad yet give me the sodium fulfillment i usually crave