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Whitney Port's little man is growing up!
The fashion designer, 37, penned a touching tribute to her son, Sonny Sanford Rosenman — whom she shares with husband Tim Rosenman — on Instagram Wednesday in honor of his 5th birthday.
Alongside an adorable clip of Sonny performing a song for his mom, she wrote, "HI FIVE! HAPPY 5TH BIRTHDAY TO MY RAY OF 🌞 , SONNY! You tested me there for a few years, but just like everything in life, anything worth having is hard work."
She added, "You're a little firecracker, and I can't wait to watch you light up this world."
As part of the birthday festivities, Port and Rosenman spent the day celebrating with Sonny. According to Port's Instagram Stories, the father-son duo had some fun waving around their toy light sabers before the family gathered for Sonny's "sun celebration" at school camp.
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In February, Port told PEOPLE that she and Rosenman are "in the discovery phase" of expanding their family and had recently met with a fertility doctor.
At the time, Port revealed she and Rosenman suffered a pregnancy loss last November, two weeks after announcing she was seven weeks pregnant with "likely another unhealthy pregnancy." Port has previously suffered two miscarriages and a chemical pregnancy.
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"We had a consultation with a fertility doctor before we had our winter break. We now go in in a couple of weeks to do the first testing, like blood testing, follicle testing and Timmy gets his sperm tested, and we kind of take it from there," she said earlier this year on PEOPLE's Me Becoming Mom podcast.
"I've been sent a list of supplements and vitamins and diet recommendations to start to get into for both Timmy and me," she continued. "I'm a little overwhelmed already, it already starts to feel like, oh my gosh now someone else is watching my life."
She added, "It's also hard for me because I just only had my D&C three weeks ago at this point, so I'm still very early in the discovery, I don't even know when the date of my last period is. You realize how much you have to get into all those details and the timing and it just becomes like a whole other job."
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