I realize this is a very old thread, but in the event the OP is still active here, I believe I have an answer to the original question of how he could gain girth for no apparent reason.
I've come to learn from a noted urologist that in some men, the tunica albuginea of the penis loses its elasticity over the years, resulting in it expanding in girth, often more noticeable in certain areas of the shaft than uniformly along the entire length. Sort of a "ballooning" if you will.
I've gained 1/2" in girth over the last 6 years for no apparent reason, with my mid-shaft girth expanding the most (sort of like a football). A weakened tunica would seem to explain this.
I would suggest this is what's responsible for those of us realizing we've gained in girth over the years without really being aware of it until we see a surprising measurement. I've found a few (not many) other threads where guys notice this, but never have I seen it explained.
Regards,
eisenhower