I agree that the best course would be to find a good naturopath to guide you.
If it were me and I were determined to go it alone I would first go back to basics and consume nothing but raw organic goats milk for a week or so. Then I would add in blackstrap molasses and free range organic eggs (the three items make for a pretty tasty drink). Next try adding some supergreen foods to the mix, such as the Dr. Schulze formula, along with some Garden of Life Primal Defense for proper digestion and healing, coconut oil and some good all around digestive enzymes such as Garden of Life's Q-Zyme.
One by one you can then add in raw or lightly steamed vegetables, gluten free grains and even some healthy meats in small portions, such as free range organic chicken and beef and especially cold water fish. I would also try a good all around whole foods nutritional product such as the wonderful intraMAX. It is pretty potent and contains 415 essential nutrients - you might want to start off with half the normal dose and work your way up.
If you notice any decline at any step along the way, eliminate what you just added and proceed along that path. Cleanses and detoxes are usually a very good idea too - but with your low weight you do not want to overdo it, in my opinion.
I hope that helps,