We're Trying to Get Pregnant.

Hanataro, the young president of a large company, is getting pestered by those around him to produce an heir, but he has neither the desire nor the time to get married. But then Kaname, his secretary and best friend, makes a proposal: "Shall I have the baby?" Kaname immediately starts taking a drug which allows men to get pregnant. However, the side effects of the drug cause a tingling sensation that won't stop...?

(Source: Sankosha, translated)