No your inability to gain weight started before you were diagnosed and may continue until things get stabilized. Without insulin glucose cannot enter cells where it's to be used as energy. As a result of that the body tries to make energy by breaking down some parts of cells which causes you to lose weight (no matter how much you eat). I think I lost 20 lbs before I diagnosed myself back in 1984. I was sort of happy to lose it without even trying back then!
If you really want to gain weight at somepoint you'll have to learn to adjust your doses based on what you eat. Peanut butter is an excellent food for weight gain, high in fat, fair amount of protein and a small amount of carbohydrates. I get through about a kilogram of it a week.
I went down to six and a half stone prior to my diagnosis back in 1981 when just 13 years old.
As stated above once I had a couple of months under my belt and had some form of control (i was lucky as my father also had diabetes so I knew the basics already) I slowly started to gain weight.
Not sure how long you have been diagnosed but if your maintaining the same weight and not continuing to lose more I would think things are already beginning to stabilize
Unless you are dangerously under weight I wouldn't worry about it. Better to be stable than gaining too much!