Anorexic & Unexplained weightgain = Freaking out

I am a 37 year old woman who has been dealing with an eating disorder in some form or another since I was about 14 yrs old. I have been hospitalized with anorexia (weighing not much & avg height) 3 times in the past 2 years. The most recent time was in March-April 2010. (I left the program after a month and had weighed 103 lbs when I left.) I did not recover...I didn't want to recover and honestly, I really don't want to gain weight right now either! HOWEVER, This past January, my husband and I separated and it has taken a toll on me emotionally. I eat a max of 500 cals per day and yet since January, I have gained 20-25 lbs! I exercise 7 days a week doing aerobics & I also walk 4 hours a day (2 hrs in the forest trails and 2 hours street walking...all with my 2 border collies). HELP! I do not understand why I am continuing to gain weight!?! I am terrified because I have already been restricting my food intake a lot more. Some days I won't eat anything. Just in the past 2 weeks I have outgrown all of my bras! I have not been this weight in at least 5 years! I am FREAKING OUT! I have to add that I also take ephedrine. (a lot of ephedrine)Last March I had a doctor tell me that "I am not 16 anymore." as the reason for the weight gain!?! I refuse to go back to her. In fact, I am terrified to go to any doctor for fear that they will tell me that I am just destined to be fat. My entire days are filled completely with weight and food thoughts. I have nightmares and end up only sleeping a few hours per night. I am beside myself! Please...Can someone offer ANY ideas as to what is going on? It just doesn't make sense and I am terrified. ***I have had my therapist tell me that I look "swollen" but no one else had said that and my ankles/feet and wrists/hands are not swollen at all. In fact, certain areas appear thinner and bonier while others...specifically my tummy, hips, thighs and upper arms...are huge! I doubt I have edema. So, what is happening to me!?!*** I feel so alone and desperate and I would rather just die then continue to gain weight. I know what being over weight is like. In 2000 I was at my highest weight of 198 lbs. I swore that I would not allow myself to gain weight like that ever again. Please help me?!?