log everything you eat. Weight loss surgery is a tool - you have to make sure you're doing your part of it, or it's not going to work. And yes - it's work and it's hard. But the difference is, with this tool, your hard work will actually pay off. But unlike what naysayers say, this isn't "the easy way out". If you're having difficulty sticking to your clinic's eating plan, then make an appointment with them. The dietitian and/or health psychologist can be of a lot of help (and if they don't have dietitians or psychologists on staff, they can probably refer you to one)
also - yes - like the other commenter said, temporary "gains" from water weight or full intestines aren't unusual. But if this "gain" lasts more than a couple of days, look at what you're eating and make sure you're complying with your clinic's guidelines.
and btw - hair loss after surgery is very common, but it's temporary. It'll grow back.