What Levels of Vitamin D should my blood show?

Patient: This question is regarding Vitamin D. I have been blood tested for a number of things, and a few years ago my doctor told me that my blood work should I needed to supplement Vitamin D because it was low. The number that came back was 17 I dont know what units they used?. He gave me a percription for Vit D and told me to take it. I am a male, 23, 185lbs and live up north in the US. What levels of Vitamin D should I be trying to get back to? I stopped taking the Vitamins the first week, upset stomach. But, I know that I shouldnt have. I feel like without some type of motivation that I will not take them daily, but if it seems too low or cause for concern then I guess I will have to start taking them again. How much Vit D supplements should I be taking, and what levels should I try to get back up to if I go back for another blood work?