Koushou Madoushi-sama Nyotai Tensei

An erotic romcom about the genius mage Alex, who after an encounter with a demon in a dream wakes up with his body irreversibly transformed from male to female. His life takes a drastic turn as he goes through female experiences such as menstruation, maternal instincts, female urination, sexual attention from men including his rival, and female masturbation.

[Summarized from DLsite]