4 lb gain 1 month? Hope not!

Last app (1 month ago) I got weighed at 11:38 am so I had breakfast but that was it.  Yesterday I was weighed at 5:15 pm...I had eaten all my meals including dinner and lots of water.  (And TMI I hadn't gone poo in 3 days). And they weighed me at 4 lbs heavier and commented on my "jump."
I'm thinking that there's no way it could be a true 4 lb gain.   😔ugh it made me feel so fat 😔