Why is this happening?

I have been a diagnosed anorexic for about a year now. I know what I should be eating (health and calorie-wise), but have only been having no more than 750 calories a day for the past 5 or so months. I've been staying around a constant 77-78 lbs for the past two months or so. I haven't changed my diet or exercise routine at all. The problem is, within the past two days I have gone from 78 lbs to 82 lbs - and yesterday I ONLY ate 370 and STILL gained. I've been eating mostly only broccoli and cauliflower lately. I know they're fiberous veggies that cause constipation and such, so could the weight gain only be temporary until I make a boule movement? Is it just bloating? Will it go away? Every time I eat I also get an awful stabbing pain in my stomach and can no longer eat. What is wrong with me? Will I be able to get back to my 77 lbs? What I REALLY want to know is HOW is it even possible to gain weight when I'm not eating enough PERIOD, when it takes obviously 3500 calories to gain a pound, while only eating veggies. It makes no sense to me. Please help.

Hi, twiggy! It could be that you're gaining weight because your metabolism is messed up now. You can't eat like this and stay healthy, please talk to a doctor. Do you think you could do that?