Jonsgurl, I go to a nutrition clinic and had my metabolic rate tested there. Where did you get yours tested? Mine was low, like yours (around 1300), but they didn't tell me to eat less. Instead, we worked on raising that number. I eat a ton of protein (literally!), do cardio 4 times a week (I'm supposed to do it five times!) for at least a half hour, and work extra hard for the middle 11 minutes of my workout. I also keep a food journal. I definitely eat at least 2000 calories every day and I've lost about 17 pounds since I started with the clinic. Before that, I ate very, very clean and exercised, but I wasn't losing an ounce--for almost a year.
Anyways, what I'm trying to say is that just because you have a low rate, that's no reason to eat such a tiny amount of calories. Everything I've read and heard says that if you eat less than 1200 calories, you're going to convince your body that you're starving. If that's the case, when you ate a ton more calories with the fries and sandwich, your body probably grabbed on to them and held on for dear life. I'm not a doctor or nutritionist, so I could definitely be wrong about that. Nonetheless, I think between the issues with the low rate, the recent gain, and your feelings about weighing yourself that it would be really helpful for you to see a nutritionist. Really.
In other topics, yes, drinking is VERY important. Uh, drinking
water, that is!
The amount you need varies per person, but looking at the color of your urine is a good gauge. The more diluted it is (i.e. the lighter in color), the more water you're getting. Clear to light yellow urine tells you that you're getting the right amount of hydration.