Does being post partum change the calories in and calories out rule?

Congrats on the babies. My youngest is 19 and getting to a healthy weight became a priority for me about 7-8 years ago. So you have a giant head start!

When it comes to food logging: make an effort to be accurate and honest with all you consume. Use a food scale for solid foods and log in grams. When a food label says 1 serving = 1/4 cup (28g) for something solid, ignore the '1/4 cup' and go by the grams. What you can fit into 1/4 cup is often more than 28g. Cups are meant for liquid measure, not solid. By the way, 28g is about 1 ounce. 1 solid ounce and 1 liquid ounce are NOT the same thing, of course. So even though 8 liquid ounces = 1 liquid cup, 8 solid ounces do not equal 1 cup in terms of food labels. It is a bit of a mess, using the same word for different types of measurement.

When it comes to logging things like eggs, bananas, slices of bread: also go by weight. I tend to eat hard boiled eggs 4-5 days each week for breakfast. The carton says large egg, quantity 1 = 50g for 70 cals. They are often 54-55, sometimes even higher. Not all slices in the bag of bread are the same thickness. If you use an entry in the database like '1 medium banana' you have no way of knowing how your banana compares to that in size. You can create your own recipes in the recipe builder, and the app/website will compute details for you. Trying to make your own lasagna and use a generic entry in the database for 'lasagna': you have no way of knowing how that actually compares to what you made, what ingredients were used, etc.

Also do account for cooking oils, beverages, etc. And if you tend to grab a bite here & there when you can (because you don't exactly have 'free' time to enjoy a regular meal) remember those have calories and add up. It might help to preportion snacks in baggies or something so you can grab a bite when you have the chance, and know what to log.

Good detective work, OP. Be patient with yourself. I would implicate hormone-driven crazy water retention before suspecting hormones altering CICO. CICO will work over time, but it will not always show on the scale in the time frame we want.