I started smoking 15 months ago. I am 20 years old now. Since that time my body has changed. I am feeling lazy all the time, I lost weight(only muscles, not fat), got weaker, sometimes having very light pain in my lungs, when I get scared from something , my heart starts beating fast and I feel light pain, like aches. And my leg muscles get fatigued and sore sometimes at night. I also feel cold when I wake up in the morning. Is that something serious and what should I do?