The nausea is almost certainly from too much nicotine -- you didn't mention the nic level you use. But whatever it is, chainvaping at that level is making you nauseated.
When you say 70/30, do you mean the traditional 70PG/30VG, or this newfangled idiocy of putting the VG first? If you're using 70% PG, it's easy to see that it's too much, because tinnitus is a common side effect of too much PG exposure. However if you're actually using 30% PG... it still seems to be too much, with tinnitus going on.
The phlegm is probably from the VG, since VG is thick, and too much phlegm is the usual side effect of too much VG.
I know you may not want to hear this... but it really sounds like the chainvaping is the bottom-line cause of all this; just too much vaping -- the PG is making your ears ring, the VG is causing phlegm -- the happy medium between the 2, and probably the excessive nic also, is to just not vape so much. (or vape at lower wattage/higher resistance, to make less vapor; and inhaling it mouth-to-lung rather than direct-to-lung wouldn't hurt either.)
Andria