I had that aching-joint thing too for a short while when I first got into vaping.
I was told that some people get this starting out due to PG being metabolised by the body into lactic acid, which is what makes your muscles ache when you work out. No idea how accurate this is but reading up on the science of it suggests it might be true.
In any event, it went away after a few days, as I recall, and I haven't had it since.
Experienced vapers all say you'll enjoy it a lot more if you drink lots of water, since PG and VG both give you a mean dry mouth. I never drank enough water anyway, so this was good advice.
Speaking of dry mouth, I just went through one h*** of a hot and humid summer without any respiratory issues. I had asthma as a kid and humidity still gives me trouble, or did until this year. I'm wondering if the dehydration effect of inhaled PG and VG helps with that.