It just may be a case of you not liking the juice. How much eliquid a day are you going through, BTW? Unless you are vaping hardy at all, that is an insanely high nicotine level for the power and resistance you are using.
Harshness can be caused by both too high nic, and also too much PG. Most sub0hm vapers tend to use a slightly higher VG percentage, however if you've been at this a while and can normally manage to vape, it's possible the flavoring doesn't agree with you, and if you were vaping different types of juices before (e.g. not fruit vapes) I guess it's possible your other flavors were muting the harshness of the nic, or something.
I, personally, love mango, and I would consider maybe diluting your liquid down with some VG to see how it performs and how you handle a lower nic level, I could see some real benefits coming out of this experiment for you... Possibly.
It just may not be a juice for you, or the juice may've been from a bad batch.
But honestly, I'm kinda more concerned about your nic level, unless you are actually just vaping very sporadically through the day and whatnot.
Best of luck,
Anna