Been very skinny all my life, diagnosed with graves disease and had total thyroidectomy last week, i really hope i can gain weight, do i have a chance?

Better chance: The presence of an overactive thyroid often leads to weight loss. Thus having a normal thyroid function through replacement gives you a better chance to gain weight. Don't worry, you will likely wish you have the same problem 30 years from now. (PS: If you are genetically lean-look at your parents' body type, then huge weight gain may not be on the horizon).