The nic absorption with e-juice is very different than it is with smoking. That said, there can be several other things going on, and without more information it's hard to tell.
Let's start with the nic.
I find that higher levels of nic and e-juice without water in it gets my throat kind of "tight". I think the nic hits some nerves, or juice dries throat out or whatever. Adding up to 10% water to my DIY e-juice helps. So does lowering nic %.
There's also PG and/or VG and/or flavoring allergies or sensitivities. These can be found out by changing juices on an experimental basis until you find one that works.
Then there's the device. A poorly performing e-cig will be harsh. Too warm = harsh. Too cold = harsh. Gunked up coil = harsh. Bad wicking = harsh.
Then there's the recipe....some vendors add a bit of "throat hit" to their juice by some means other than the nic.
Really, it's hard for us to tell. What device? What level nic and PG/VG? Try different vendor?
Just some ideas.