Hi everyone! My weight is fluctuating . . . it was back to 155 this morning!

I'm hoping it's just water weight.
I had my blood drawn for a cholesterol test this morning (first time I've had it tested ever!), so I had to do the half-day fast (not eat after dinner and not eat in the morning before my test). Man, I was starving this morning! I don't understand how so many people can skip breakfast - my stomach wakes me up bright and early! Anyway, my veins are really hard to find, but I got lucky today and she got it on the first try, woohoo! So as soon as I was done I went to Au Bon Pain to get some breakfast, but I was bad . . . I should have gotten a yogurt cup or something, but instead I got a bagel and egg sandwich, with cheese! At least I restrained myself from getting the bacon, and I got it with egg substitute. But still, that plus orange juice was about 550 calories.
I'm a little worried about getting the right amount of calories in a day. I try to get between 1200 and 1500, sometimes I go over but I almost never get above 1800. I think I need to stay around 1500 in order to lose weight. Anyway, I use fitday.com sometimes but I'm bad about keeping track every day, but yesterday I just barely had 1200 calories, which really surprised me. I thought I had been eating more than that usually, and yesterday was a pretty normal day for me. It makes me wonder if my body is doing starvation-mode or not. On the other hand, this weekend I had two meals at a restaurant and half a milkshake in one day, which must have been at least 1800 calories.
Man, this dieting stuff is hard. I was so sad to see the scale move in the "wrong" direction this morning! I refused to change the sliders in my sig because I'm hoping it will go back down in a couple days.
Sorry for the long post!