NEW YORK -- In just four years, Justin Bieber has gone from fielding innocuous questions about his haircut to denying that he's in desperate need of rehab. Bieber's grown up and into tabloid territory, with his recent troubles making some question whether he's just the latest teen star gone wild.

In what could have been his worst week ever, the 19-year-old pop star struggled with his breathing and fainted backstage at a London show, was taken to a hospital and then was caught on camera clashing with a paparazzo. Days earlier, he was booed by his beloved fans when he showed up late to a concert.

Those incidents come after photos of Bieber appearing to smoke marijuana hit the Web, and some headlines have suggested that the ultra-popular star is going through a famous Britney Spears-style meltdown.

Others suggest he's struggling with a more common condition: being a teenager.

Donnie Wahlberg, who was just 14 when New Kids on the Block debuted on the music scene in the late 1980s to wild fan craze, said he remembers the pressure and hard times that came with being a teen celebrity.

"Justin Bieber's making mistakes that everyone makes and he's probably trying things and exploring things that most kids his age explore, but the problem is he's got 50 paparazzi chasing him around when he does it," 43-year-old Wahlberg said. "When we are 19 and 20, we think we can take on the world and we do forget that there is a lot of life left to live in front of us, and hopefully he'll get through these times and find his way into a long career and a healthy adulthood."

Bieber, his manager and his mother didn't respond to interview requests for this story. But the pressure was evident in the days following his collapse backstage at the O2 Arena, as the Grammy-nominated singer wrote on Instagram that he's sick of the "countless lies in the press" and that he would not be heading to rehab.

"I've accomplished more than I could've ever dreamed of, i'm 19 and it must be scary to some people to think that this is just the beginning," he wrote. "I'm a good person with a big heart. ... All this isn't easy. I get angry sometimes. I'm human. I'm gonna make mistakes."

Even mistakes seem like new territory for Bieber: Since breaking out at 15 he's seen five of his albums hit No. 1 on Billboard's 200 albums chart and nearly 20 songs crack the Top 40. He's had several world tours, launched a massively successful 3-D movie about his life and made deals that include his own dolls, nail polish and fragrances. He's got a social media presence that includes 52 million likes on Facebook and 36 million Twitter followers.

But does that leave any time to be a kid?

Nick Carter, considered the wildest of the Backstreet Boys, was also the group's youngest member when they began to dominate the music charts in the 1990s, and he recalls the days when he grew mad as an overworked teen who yearned for a normal life.

"I remember getting tired. I remember getting burned out and I'm like, 'Let me relax' and you have managers, and the record label ... and then before you know it, the artist gets resentful and starts to revolt against them and that's when you end up with a situation like what's going on," he said, referring to Bieber.

"In a lot of ways you're resentful and you're missing out with your friends, your childhood, you see all of your high school friends growing up ... and you're like, 'Oh, I got to go back on tour.'"

Vincent Herbert, the record executive who signed Lady Gaga and also discovered the teen R&B boy band Mindless Behavior and singer JoJo at 12, said that young singers need role models around them who are fit, and that there must be "time for music and time to be kids."