08/07/2009 at 03:40 PM EDT
her son Bronx Mowgli, now 8 months, Ashlee Simpson-Wentz
was prepared for an uphill battle when it came time to shed the pregnancy pounds and regain her figure.
But she was pleasantly surprised to find that she quickly bounced back with little effort on her part, she tells PEOPLE's Celebrity Baby Blog.
"After I had Bronx I lucked out," the actress-singer admits. "I mean, I’m 24-years-old, [I have] the genes from my mother and I did work out for three months."
With the new mom busy on the set of Melrose Place
and husband Pete Wentz
on tour, help for the couple comes in the form of grandparents.
Between her mother-in-law Dale, who offered up "great advice on his sleeping schedule" and her own mother Tina, who spends time with her daughter and grandson on "a daily basis," Simpson-Wentz’s support system is stronger than ever. "[My mom] is an amazing grandma, they both are," she notes.
So what will the new mom need Tina's assistance with next? Teething.
"Right now Bronx's got six teeth that just appeared," Simpson-Wentz revealed. "First two, then four, and now six in just a few days!"
Reporting by SCOTT HUVER
For more from the interview, visit PEOPLE's Celebrity Baby Blog