Just quit smoking.
When you quit, it hurts. Nicotine is like an anesthesia, when you stop, you feel pain in your lungs. Since you've cut back, that might be why. I *lightly* smoked about 10 packs for about 4 years. When I quit, it hurt, and it scared me. Nobody seems to discuss it, but it's very common to have lung pain after quitting. After about 3 weeks, it cleared up but it was scary to have that pain for so long.
But just quit. It's not that hard. You'll have mood swings, and you'll have a *desire* to smoke every now and then, but you ultimately decide what you do and you don't ever have to smoke. You just have to decide to give it up, and never forget, the reason you feel so lousy is from smoking. If you go back to smoking, you're right back to screwing up your body.