As often the case, a vaping "side effect" needs to be figured out through a process of elimination...
POSSIBLE factors for an irritated through you can test -
Is it PG? Try high VG juice.
Do you vape "hot"? Try longer tip, or more airflow, or something to cool the vape a bit.
Is it the flavoring? Try different juice.
Also could just be "acclimating" to vaping all day. And the fact is that you are also likely to have some OTHER symptoms from NOT smoking.
But CONGRATULATIONS!!
Stick with it and figure this stuff out - you'll feel better, and breathe better, SOON.