You're right actually. Unexpected numbers on the scale can be caused by many factors, and it's frustrating and disappointing for sure. There are a million things that influence that number. The average person fluctuates 0.5-2lbs over the course of the day. If you want a better idea of what's actually going on - try weighing daily - same time, same scale, same clothes and average it instead of having one number, which is just a snapshot of your body at that specific moment.
Then there are still other things to consider:
Muscular Repair from increased exercise
Amount of water you've had
Amount of sleep you've had
If you are sick or your body is fighting off illness
Time of day
How much coffee/caffeine you've had
How late you last ate
Reaction to meds
Reaction to foods
Sometimes it's about going back to basics. The first thing to check is are you tracking everything you should, not by eye (portion distortion is real) but actually weighing and measuring?
Are you eating enough calories? Eating too few can create a sluggish metabolism that holds onto everything. Not sure? If you are a PRO member, you can track calories alongside points by turning on the Secondary Metric under your Settings.
Are you using your 0 Bite foods correctly? Do you have the right food list and understand how it works?
Are you getting enough water? Hydration is key to not only stopping hunger but keeping your body from holding all it can from the foods you're eating.
Check in on your sodium levels. For sodium sensitive people - you can gain 2-8lbs overnight from retention. And high sodium hides in many things as innocent as canned soups, frozen dinners, cottage cheese - and when you eat out - it is very easy to exceed your daily recommended level. The average person shouldn't exceed 2200-2400mg/day and people needing to watch sodium, it's 1500. A large Wendy's Chili for example = 1170mg. McDonald's Grilled Chicken = 1110mg. Applebee's Fiesta Lime Chicken = 3970mg...
For most people it will take 1-2 days to flush through your system - so be sure to watch this 3-4 days before weigh in to avoid a big surprise. The good news is - it isn't a real/fat gain and drinking plenty of water (without additives - you'd be surprised at the sodium in some diet drinks and products) will usually take care of it for you.
In the end, this is a long haul process - some weeks up, some down. Be patient with yourself... It will balance out. #justkeepswimming