When to say no?

When a loved one continuously asks you for money, when do you say no? I’m 22, work two jobs (sometimes three) to provide for myself and after paying my bills and tuition for school, I don’t have much money left over each month. Whatever I do have left over, I would like to treat myself to a nice dinner, save it for a rainy day, or get a new shirt but can’t because I’m always helping this family member out. Right now I’m stuck thinking about how I know I’m not obligated to help them but I will feel bad if I don’t. But at the same time, I know I can’t keep going without what I would like from helping someone else out. So when is enough, enough and when do you tell a loved one you are unable to help them financially? (I’m hoping that over time/soon telling them no will get easier for me)