I had the same symptoms shortly after I started vaping. Strange that it didn't happen immediately, but rather a couple of months down the road. I switched to 100% VG juice, and started drinking about 64 oz of water each and every day, and the problem went away. Over the first six months or so of vaping various little issues would pop up and make me question what the heck I was doing. All of these issues have long since passed now and I've got about 16 months of vaping experience on my side.
Different juices, even at your perfect PG/VG ratio level, can cause some different issues. As an example, I have asthma, usually fairly mild. About three months into vaping I started having some asthmatic-type issues. I started noticing where, why and when they occurred, and what juices I was using. I experimented with different juices and have found some that I love that cause me zero asthma issues. Whereas other juices can cause an immediate reaction in my breathing. Plain Blend 4 from AVE causes this problem for me. But, the same Blend 4, mixed with other flavors, or even a little bit of menthol, is problem free. Gorilla Juice and Boba's Bounty can sometimes, but not all the time, cause me some problems, so I vape them sparingly, usually for a brief change of flavor to prevent burnout. Peach Hype from AVE and Tennessee Cured from JC cause me zero problems, and they are my primary vapes. I have many other juices that are problem free as well, far more than those that cause problems.
My point in all of this is that you have to find what works for you. If you want this to work, there is probably a way to make it work. There might be some trial and error involved, but if it keeps you from smoking it's worth it. In November 2011, I had three stents put in my heart, my blood pressure was consistently around 150/90, sometimes higher. My blood pressure now is consistently around 118/70. November 2012, I had a complete physical, with nuclear stress test, body scan, x-rays, etc., my numbers were all great, no problems to worry about (other than the colonoscopy coming up at the of them month, my first). And, as a side benefit from all of the water I drink now, my sinuses are better than I can ever remember.