I'm 17 and I started smoking, I really feel bad about it?

[ChiliSauce]

I'm 17 and I'm a freshman in college, and I have 28 units and its just so stressful! I'm really working hard, but all I get is like average grades. Its so frustrating. My older sister told me that when I start college, it's normal to smoke cause it's stressful. And I tried smoking, and it really does help! Now I feel like I'm starting to get addicted, the first time I had cigs (like a 2 days ago) I had like 5, and today I had 2, one during break and one after class. I feel bad because my family has a history with lung and colon cancer, and I know smoking is bad for me since it makes teeth yellow and I'm already lacking in calcium, I mean I think I am. But I kinda don't want to stop because it really helps me deal with the stress, I can't just 'work out' to deal with stress or other things cause there's no time! I have to study all the time, like I wish I didn't need to sleep just so I can keep up with work..