I have a hard time eating enough.

It may be time to see your doctor again. 500-700 calories are not nearly enough to sustain your vital organs.
You have a serious problem and you must take care of it.

I have a hard time eating enough as well, mainly because I'm not hungry. You should really force yourself to eat 1200 a day and if you want to lose weight, exercise moderately every day. Just because you're losing weight "like you're supposed to" doesn't mean you're doing it the healthy way. Log what you eat and find foods you like and how much you need to add in to meet your calorie goals. Add in snacks between every meal to help up your calorie intake increase.

Remember just because you're losing weight now does not mean you'll continue that path. Eventually you'll have to eat less and less to continue your kind of weight loss and that is NOT HEALTHY. As a person who was hospitalized for anorexia you need to be even more careful and even force yourself to eat more. Make multiple meals/pack snacks to eat throughout the day/put alarms on your phone to remind you that it's important to fuel your body.

My favorite snacks to boost calories are granola bars or whole grain bread. Since you're a vegetarian it's also good to eat healthy oils and protein rich foods. Make beans or when you cook things add coconut oil. It'll help a bit.

Good luck and don't let yourself slip back into those bad habits.

I'd suggest trying to snack on nuts throughout the day to up your calories a bit. And try to get into the habit of always eating lunch at the same time, say 12, so you'll eat something every day even though you never feel hungry.
Also make sure to eat fullfat products.
Avocado is good to up your calories.
Basically try to eat more calorie dense food.

And I agree with the other posters that think you should probably talk to a professional, especially since you have (had?) anorexia.

I'm having the same problem, I didn't even realize it until i started logging my food with MFP. What I've been doing is trying to eat more frequently instead of more at one time. For me it helps to just get calories spread out through the day for energy, without feeling sick trying to eat too much food at one time.
I never feel hungry throughout most of the day, and rarely ate any breakfast or lunch but try just having something small. Now I try to have a yogurt or some fruit in the morning, and it really does help. And I know it's hard to want to eat when you aren't hungry or feel guilty about it, but for me at least if I make myself eat a little something, I realize my body did actually want food.

For more of a mindset aspect, I find it really helpful to stop thinking about calories as fat, but as energy And for a goal, think about instead of being "skinny" being fit. Focus on how you feel instead of numbers, calories or on the scale.
If being healthy and feeling good isn't enough motivation focus on what you are really aiming for. When you think about the body you want to achieve, is having more about having your ribs show or a toned stomach? Hipbones showing or a nice butt?

Sorry for this being so long, but this is just what has worked for me. Reevaluating what I really wanted has motivated me to try harder to change habits. I realized losing weight is not what I really wanted, what mattered more was feeling better and looking in the mirror and being happy with how i looked. Focus on your goal and even when you don't want to eat, that you need it.