In my opinion, 50 mg is way too high! Regardless of the effect on your throat, it is simply too much nicotine. If you feel in that much of a need for nicotine to kill analog cravings, I would suggest trying swedish snus (getsnus.com). It is likely that it is other alkaloids found in tobacco that are what you are craving, and more nic will not help...and that is too much nic! Generally 36 mg is about as high as we would recommend safely, and even that should not be all the time.
As for your throat, yes, that much nic can irritate the throat. It could also be that you are vaping PG or mostly PG juices, and the PG is causing dryness and irritation. This is quite common. The solution is to try some VG juices. It might be that you can do a juice that has some PG in it, but to really isolate this to cause, other than lowering nic, is to go with VG juices at least until you see. PG certainly does this to me, and I vape around 12 mg normally. Vaperite has some excellent organic VG juices. The Kona Cream is delicious. I suspect this is most of your issue.
High-power vaping high-nic juices can also irritate the throat. You could also be getting a cold, of course.