Expecting You by Claire Cullen

Lost—one precious embryo. If found, return to Beckett Rayne, worried alpha father…
Beckett has one last chance to save his son—by giving Luca a sibling. But the clinic makes a fateful mistake: they implant the embryo into a stranger. With Luca running out of time, Beckett will do whatever he can to find his unborn baby. The only light in this crazy situation is Zac, their new nanny. Sweet, funny, and a good listener, he’s the best thing to happen to their little family in a long time. But as they grow closer, Beckett starts to fall for him, and risks ruining everything if he can’t keep himself in check.
“Only you could walk into a clinic for contraception and leave with a baby.”
All Zac wants is to be able to hold down a job, unburdened by his wildly erratic omega hormones. With the help of his best friend, he gets the implant he needs to put his life back together—or so he thinks. Now that everything is finally falling into place, he takes a position as nanny to a new family: Luca, a little boy who needs a lot of love, and Beckett, a lonely alpha father with the weight of the world on his shoulders. But Zac is at risk of breaking the first rule of nannying: never fall in love with your employer. And then he discovers the impossible: he’s pregnant.