Just checking the conjugation of the verb 'to sneeze'...
Is it: å nyse, nyser, nøs, har nyst??
å nyse - nyser - nøs/nøys/nyste - har nyst
nøs is probably the most common of those.
If you haven't already discovered it the ordbok at http://ordbok.uib.no/ gives conjugations to words.
The three options for conjugating the preteritum provided by fveldig are shown, less clear is when each option may occur.
Why can't it be "was sneezing"? I know it has far fewer uses but it's still a thing..
I fail to see how you could possibly combine the perfective 'fourteen times' with the imperfective 'was sneezing'.
Could you elaborate?
You can't say "He was sneezing fourteen times" in English and be grammatically correct. So Duo isn't going to accept it here either.