I had the same thing, it stopped after about 4 months. I could only sleep on my back at the stage you are at now, but one night I must have turned over in my sleep. Both my wife and I woke to the sound of a very loud crack. I still have no idea what it was but there was no pain involved. I also had lots of skin sensations around the scar area, where the nerves were mending. I could feel the signals getting confused. One minute it was hot, then cold and then suddenly like someone was stabbing me with needles. I also used to feel a cold/wet sensation like fluid was running down the inside of my chest, like a vessel had burst. When the stiffness starts to really wear off, mine was around 6 months, then all the wierd sensations stop. Everyone heals at a different rate, and being only 47 at the time I thought I would be back to normal in no time. It took 12 months for all pains to fully stop with me. Your chest will be as strong as it was before, it not stronger because when bone knits together it forms a very strong bond. For the first six months it felt like my lung capacity was much smaller, like my chest couldn't expand as much as before. You have a lot of recovery to go yet, but you will get there. The best exercise I found to help recovery was deep breathing. Take a slow deep breath as far as you possibly can, then hold it for 5 seconds and slowly breathe out. Do this 10 times and repeat three times a day. It works wonders and gets things moving.