Jessica Simpson to Wed Eric Johnson After Baby

Eric Johnson and Jessica Simpson

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It's been a whirlwind year for Jessica Simpson, who became engaged to former NFL player Eric Johnson last November and recently confirmed that she's expecting their first child.

"They're really excited," a source tells PEOPLE of the pregnancy. "It wasn't something they planned per se, but it's also not something they were trying to avoid."

Still, it did cause the couple to put the brakes on planning their wedding, which will now probably happen after the baby is born.

"They're both still really committed to getting married, and were both really into making decisions about what kind of wedding they wanted," continues the source, who adds that the nuptials were originally set for this month.

"It's just going to be at a later date now [because] they really want to enjoy this time in their lives."

And despite tabloid reports that the couple is expecting a girl, another source confirms to PEOPLE that they don't know the sex of their baby.

But whether they have to stock up on blue or pink onesies, "they're both very family-oriented and having a baby is something they both wanted," the first source says. "It's wonderful!"