Omega wa Bed de Uso wo Tsuku

Rio Shinomiya, the third son of a major pharmaceutical company who has been living a prosperous life, has a secret. All Shinomiya's sons have been known to be born as Alphas, but only Rio has to live with hiding the fact that he is an Omega. He's been living his life knowing that the heat will come and therefore has to take an suppressant. But when the first lust comes...

(Source: pixiv, translated)