My guess is that with figures like those you quote you must be a T2 diabetic, not very bad, but T2 nontheless.
There are other thin T2 on this forum, I am not amongst them but I keep on trying.
I did see a TV program that claimed it was not the visable fat that caused T2 but the internal fat aound the liver etc.
Maybe you are like this?
AS "Denise" says eat more calories as fat, eat plenty of protein, and eat plenty of lowish carb vegetables.
Eat some fruit but not to much. Check to see how many calories you have consumed each day and make a written record.
You need around 2500 calories a day to mantain weight more to increase it.
H