Any advice??

I was anorexic about 5-6 years ago. After about a year, I returned to a healthy weight and was satisfied with it. Six months ago I was diagnosed with Postural Orthostatic Tachycardia Syndrome (POTS Disease), and was told I could no longer run or do any other sort of cardiovascular activity. 
I'm a 21 yr old female, 5'6 and 1/2" and weigh about 118 lbs. Both me and my doctors are satisfied with this weight. When I was running I was eating about 1600-1700 calories per day and running 2-5 miles 6-7 days a week. However, to make up for my lack of exercise, I am eating only 800 calories to maintain this weight. I know this is too low, but I don't know how I can eat a more acceptable amount of calories without gaining weight. I'm afraid that if I start to gain weight, my anorexia will kick back up due to my inability to control my exercise habits. I'm eating healthy - carbs, veggies, and lean meats. Also, I do eat five small meals a day - that was also recommended to help reduce my POTS symptoms. But I know that 800 calories is too low. 
And I should probably clarify I don't want to take any sort of pill or follow some ridiculous diet. I just want to eat balanced meals at a normal caloric range.

What would be the best way for me to start increasing my calories?  How much weight should I expect to gain? Also, any idea how long it will take before my metabolism will get out of starvation mode and start burning some excess calories??

Thanks for any advice you give :)

I was anorexic on and off for almost ten years, and have been in recovery for the past 2 years. I was eating about 800 a day when i was at my lowest, and my doctor threatened to have me committed to rehab because I was slowly killing myself. that was my wake up call.

I'm 5'7 and 130 now (heavy bones and a medium build) and that's about as low as I'll go ever again. As soon as I stopped starving myself i gained weight, about 10 pounds over 2 months and then it plateaued to about 2 pounds a month until i hit my goal and now i'm trying to maintain.

Start slow. move to 1000 calories and do that for 7 days to let your body adjust. then move to 1200 and maintain that for 10 days. bump that up to 1400 and maintain that for 14 days, then try 1500 and keep that for 10 days. in about 6 weeks you'll be at a more normal range and then you can adjust it up on your schedule.

gaining weight back is scary, and not being able to excercize makes it harder. I am/was a runner and was diagnosed with cervical cancer during my recovery and wasn't allowed to do anything for months and i slipped back into old habbits again.

you just have to tell yourself that the number on the scale means nothing. it's how you feel in your body. If you feel like you fit in your own skin and you're comfortable that's what matters. I sure as heck didn't feel comfortable when i was so bony i would buise my arm on my hip bone if i rolled over on it at night. Now i'm comfortable.

You'll have your days when you feel big and you'll want to restrict again, but try to remember that everyday our body changes and when it comes to your health a few pounds more is better then a few pounds less.

hope this helps, good luck!