Advice/Help, Please???

My eating habits vary dramatically, week to week or day to day. I've lost about 40 pounds since the beginning of the summer, and I'm suspecting that I have some sort of E.D, too.

Yesterday, I ate about 1,000 calories and today, I've eaten nearly 3,000. I'm binging on coconut cake as I type these words.

Help!! Any advice? I don't want to become anorexic and get sick, but I feel so fat if I hit 1,000 calories in a single day. Some days, I've been able to eat just 600 calories without any side effects....but now, I become constantly tired, depressed, and distracted if I eat only 600.