Drink lots of water! Microtears in your muscles means you hold onto more water after exercising. The more you drink, the better you flush out byproducts like lactic acid.
You're hungrier because your metabolism gets ramped up. Eat something with complex carbs and protein (small) before exercising, so you're not running on empty, and have something small again within an hour or so of exercising (to help fuel muscle rebuild!) As long as you're eating healthy food, in decent proportions, you're doing good.
I've noticed that I flux up and down quite a bit... as long as my overall progress is towards the "down" I don't freak out too much. For example, 2 days ago I was able to move my ticker to 183.4! The next day, my weight was 185.6 and didn't want to budge. This morning? 182.8 and holding steady.
I'll go for a few days at a higher weight, and then drop back down again... it's if I go at a maintained higher weight, and then increase to ANOTHER higher weight that I know I'm genuinely gaining.