In a blog post last week, Campbell wrote that while her lungs are doing a good job of producing oxygen, her blood "isn’t doing a good job of carrying that oxygen."
Her doctors think the problem might have something to do with her kidneys, Campbell wrote.
"If you see me in person I look pale sometimes and I get tired easily. So, I have to be careful to rest enough and, interestingly, drink enough water and juice (yum). Having spiffy water bottles is my new thing," Campbell wrote.
On Twitter Thursday, where Campbell got the attention of pop star Justin Bieber months ago, Campbell wrote: "Guys, we need to give my kidneys some pep talks … or some pep tweets! They're not really doing their job, silly looking kidneys!"
Transplant surgery took place in April
Campbell was diagnosed a year ago with idiopathic pulmonary fibrosis, an incurable and degenerative lung disease. She underwent transplant surgery at Toronto General Hospital in April.
She made international news with her high-profile campaign to raise awareness of the need for organ donations. Among other things, she appeared on the Ellen DeGeneres Show.
Ontario's Trillium Gift of Life Network has credited Campbell's efforts to a noticeable spike in new registrations for organ donors.
And in May, she was awarded the Queen's Diamond Jubilee Medal for her campaign to raise awareness for organ donation.
Speaking events, book plans
At the end of her blog post, Campbell said she plans to continue her organ donation advocacy work and is writing a book about her experience.
"In Ontario alone there are, right now, over 1,500 people waiting for a second chance at life through an organ transplant. Every three days one person on the transplant waiting list dies," she wrote.
"I am sad to say a very dear friend of mine, who was on the transplant list, passed away in July; she was 20 years old. I am dedicating this post in her memory. She, along with many others, fought an amazing fight and kept hope until the end."
Campbell also said she's still planning on a victory dance on the Ellen show.
"They still plan on having me shaking and groovin, it's just a matter of health. I want to dance at my BEST. Ya know?" Campbell wrote.