Your weight can fluctuate several pounds during the course of a single day. Some like to weigh every morning and familiarise themselves with the daily changes and others like me, prefer not to do so. I usually weigh myself no more than once per week on the morning after a fast day. If you are constipated, have eaten well in the past few days, or your body is retaining fluid which it can do after vigorous exercise or with certain medications, you may not see a loss on the scales immediately, and in my experience it is not a regular loss. I’ve lost nearly five stones and some weeks I lost two pounds and others none at all despite not doing anything different.
I am guessing that your gain is food in transit after three normal days followed by one fast day. Stick to Fridays, why fix it if it aint broken ?

I’m a little bit addicted to weighing myself. If I don’t hide my scales, I will get on them several times a day, but I only record my weight once a week, every monday morning to give me an overall picture of how its going.