When Janelle Brown and Kody Brown’s son Garrison died suddenly in March, she and the rest of the world were left in shock.

Speaking exclusively with PEOPLE, the Sister Wives star, 55, opens up about that devastating day and why she was blindsided by Garrison’s heartbreaking death by suicide at 25.

“We just had no idea that he was in that place,” Janelle, 55, tells PEOPLE, adding that “substance abuse” likely played a role in his state of mind before his death. “But he didn’t ever express any kind of extreme sad feelings.”

“In fact, he was very funny, very upbeat,” she adds. “He had a career path that he was excited about. He had a life, he had friends.”

On March 5, Garrison was found dead in his home in Arizona. At the time, Lieutenant Charles M. Hernandez II of the Flagstaff Police Department told PEOPLE that officers responded to a report of a death inside a home and confirmed that Garrison’s brother Gabriel, 22, had “discovered Mr. Brown deceased.” Officials later ruled his manner of death as a suicide.

Janelle says she and her family members “never had any idea that it would go this way,” noting that there weren’t any obvious warning signs and Garrison frequently spoke to family. Towards the end of his life, she says her son checked in with his loved ones, had adopted another cat and felt “really excited” about his career prospects.

“We actually were having conversations. He had all the resources that he could have needed,” she recalls. “This was just such a shock. We just never expected this.”

“I really actually had sort of thought like, ‘Okay, maybe he’s finally starting to get his momentum,'” she adds. “It’s hard in your twenties to find your path. And I was really excited, so it was such a shock… because there was just no indication at all.”

The Sister Wives star, who will return to TLC screens for season 19 on Sunday, Sept. 15, also believes “a lot of young men his age” suffer from mental health issues that never get addressed.

“We should be speaking more, especially about mental health for men, and that there’s no shame in getting help and seeking help,” she says. “We just had no idea. This was such a shock to us.”

Now, Janelle and her family members do “real check-ins” whenever they connect.

“We’re very real and we assess,” she explains. “Life situations come up and we’re always like, ‘Okay, so what about mental health?’ We actually say the words and we wait to hear what’s really happening, not just kind of gloss over it. I think we’re definitely putting more stock in mental health in our family.”

Still, Janelle acknowledges there wasn’t much more she could’ve done as a mother to prevent this tragedy.

“I don’t know what we could have done different[ly],” she says. “We were definitely — and I would encourage everybody to be that way — we were having real conversations with him. We were offering resources, we were always talking to him, we were loving him. All the things were there. It really just was something he could not… like the demon he couldn’t get on top of the battle. He couldn’t seem to get over.”

“It just wasn’t for lack of love or lack of anything. And all I can do is think… we always ask ourselves could we have done something more, but I don’t know,” she adds. “I think that’s a grief trap because I think, ultimately, everybody is responsible for their own actions and their own decisions. But we did everything. We really did everything that we could have done. And unfortunately, sometimes [that] still isn’t enough.”

Shortly after news of Garrison’s death in March, Janelle and Kody shared a joint statement addressing the news on their respective Instagram pages.

“Kody and I are deeply saddened to announce the loss of our beautiful boy Robert Garrison Brown,” Janelle wrote in the post. “He was a bright spot in the lives of all who knew him. His loss will leave such a big hole in our lives that it takes our breath away. We ask that you please respect our privacy and join us in honoring his memory.”

Janelle has since paid tribute to her son on multiple occasions, including recently on what would’ve been Garrison’s 26th birthday. “We are missing you terribly today. It’s hard to believe you aren’t here anymore,” she wrote in April. “I still feel you nearby sometimes. And I’m grateful we will see each other again when my journey is completed.”

Garrison had been a part of TLC’s Sister Wives since its debut in 2010. Now-exes Janelle and Kody also share daughters Maddie, 28, and Savannah, 19 as well as sons Logan, 29, Hunter, 27, and Gabe, 22.