I guess it depends on what normally happens when you get your TOTM. For me I usually start retaining water about 5 days before i'm due and I look puffy in the face and then as soon as its over it all drops off. I've noticed I can gain between 3-5lb coming up to it and then it goes away about 3 days into it. Are you a daily weigher? Maybe ditch the scales till your weigh day when you have your TOTM.
When I did exante last year I got my TOTM in the first week and I didn't lose a single lb, and that was the first week when losses are the greatest, I was gutted!
So yeah it's normal to sts or gain when it's your totm. The week after loss should be a biggun though, mine was.