The best way to investigate your health is always with the assistance of a doctor. If you are not certain you can make an objective ascertation, ask them if your weight is within the healthy range. You can also ask for bloodwork to be done to ensure organ function and electrolyte levels are healthy. (It is entirely possible, for instance, to be an average weight, but be malnourished, or other problems)
If you are feeling uncomfortable with your body, or are concerned about engaging in exercising with healthy limits, you should definitely bring these issues up with your counselor. Body imag and eating/food issues are very serious, but you shouldn't be afraid to talk about them. I wish you luck in successfully overcoming these and any other obstacles you have.