The oxford english dictionary disagrees with you.

https://www.oed.com/search/dictionary/?scope=Entries&q=ooh

"Ooh" is most certainly a word. As is both "Ah" and "Aah" https://www.oed.com/dictionary/ah_int?tab=factsheet#8068455

https://www.oed.com/search/dictionary/?scope=Entries&q=aah