Questions & Answers about Forkjølelsen gjør meg trøtt.
Norwegian usually puts the definite article at the end of the noun instead of in front of it.
- en forkjølelse = a cold (indefinite)
- forkjølelsen = the cold (definite)
In this sentence you are talking about a specific cold that you currently have, so the definite form is natural:
- Forkjølelsen gjør meg trøtt. = The cold (that I have) is making me tired.
If you wanted to talk in general, you could say:
- Forkjølelse gjør deg trøtt. = A cold makes you tired / Colds make you tired (in general).
Forkjølelse is a masculine noun in Bokmål:
- Indefinite singular: en forkjølelse (a cold)
- Definite singular: forkjølelsen (the cold)
- Indefinite plural: forkjølelser (colds)
- Definite plural: forkjølelsene (the colds)
Because it’s masculine, the definite singular ending is -en.
If it were feminine, the definite could be -a (e.g. ei jente → jenta), but forkjølelse is treated as masculine, so you say forkjølelsen.