I think for starters, you telling us that you don’t sleep, eat always at night, pretend everything’s great and smoke a pack a day indicates to me that you already know where you are going wrong...
You're not taking care of yourself. You dont love yourself and you're trying to get that love from others around you through doing what they want and trying to make sure they're happy before making sure you are...
I honestly cant say you are exactly depressed as much as i can say you just have a really bad mindset... I cant say what from, perhaps your parents, your friends, yourself...All i can see though is you are sad and lost, not depressed. Because anti depressants wont get you anywhere, they wont help you open your mind UNLESS you have been struggling with this for most of your life...Than maybe you do have a chemical imbalance and need professional help. But as far as i can see, you're what 18? you're a teen that has perhaps been through a lot and needs someone to talk to and needs to learn to help themselves and needs to want to love themselves. If you dont want to you wont get anywhere..
Please note that pills wont get you anywhere except make you feel happy. thats it. that wont help in the long run and if you really really want to get better, quit smoking, go to bed at better hours, or just get more hours, eat more often, dont pretend but actually try to make things better and if you already are trying to make things better, dont pretend, its ok, know whatever is bothering you is not okay and let them (other people) know it too. No more hiding, its ok to be you and love you. PS: I know quitting smoking is difficult, i used to. (hence the word, used)
I hope this helps you and opens your eyes, if you need any more help on the matter, feel free to inbox me. And if this didnt help...*shrug* sorry, i aint no professional. Just someone that gives a damn.