it feels like a forever

There is this subtle but insidious feeling deep in my lungs. It is almost like an itch that you can not scratch, but diffuse. To distract myself I have taken to drinking diet coke, or eating food with strong flavours. There is a risk of getting fat from this, and I know if this happens I will start smoking again. The thing is, smoking suits my angst and creativity. On the other hand looking and feeling good are essential. The only other thing that scratches that itch, at least temporarily, is exercise. Today I went for an hour-long run and I feel great, though the itch is slowly returning. How long will this last? It feels like a forever.