"I never imagined my life would be like this," 17-year-old McKenze Messman tells PEOPLE

Fifteen-year-old McKenze Messman was living every teenager’s dream during the summer of 2015. The soon-to-be freshman at Waverly High School in Waverly, Nebraska, was spending her days at the pool, waterskiing on nearby Johnson Lake, and going to cheerleading practice three times a week after landing a spot on the varsity team.

“I was having so much fun,” McKenze, now 17, tells PEOPLE in this week’s issue out Friday. “I couldn’t wait for what was next.”

But just three days into the school year, life as McKenze knew it would never be the same. What started off as small allergic reactions that would send her to the nurse’s office, soon turned severe and life-threatening. During the next three weeks, she went into anaphylactic shock seven times and was rushed to the emergency room.

After months of testing, she was finally given a diagnosis: Mast Cell Activation Syndrome, an incurable condition where mast cells in her immune system malfunction, causing her body to have extreme allergic-like reactions to a range of outside triggers.

“I’m basically allergic to everything,” says McKenze, who was subsequently diagnosed with two more disorders, Ehlers-Danlos Syndrome (EDS) and Postural Orthostatic Tachycardia Syndrome, after numerous doctor’s appointments and a 10-day stay at the Mayo Clinic in Rochester, Minnesota.

The three together — called a trifecta — create a “perfect storm” of relentless and debilitating symptoms, including fainting, seizures, stomach cramps, muscle weakness and crippling fatigue.

“Patient’s have symptoms from head to toe,” says Dr. Tania Dempsey, an expert on the syndrome.

McKenze has over 100 triggers — which include everything from dozens of foods to cleaning supplies, and even the weather. And because of the EDS and POTS, she has issues that range from seizures to fainting and joint dislocation. She typically wears a protective mask when she leaves the house and uses a wheelchair so she doesn’t fall.

“It’s a lot,” she says, “and if I get stressed or excited I will have a reaction. My triggers also change every day.”

McKenze’s ‘New Normal’

McKenze was forced to leave school because she couldn’t stay awake in class, and now takes online classes at home. She’s on a regimen of up to 21 medications a day, and three times a week she gives herself an infusion of saline fluids in her blood vessels.

“I feel better for around four hours after that,” says McKenze who typically sleeps around 15 hours a day. “That’s when I get to leave the house.”

It gives her energy, and for those brief hours, she feels like her old self.

Watch the full episode of People Features — McKenze Messman: Allergic to Almost Everything, streaming now on peopletv.com, or download the PeopleTV app on your favorite device.

McKenze Messman
| Credit: Sam Comen

And although the days of being in the water with friends and taking vacations with her family are now just mere memories, she can still find joy in meeting friends at the local mall and grabbing a drink at Starbucks.

“This is my new normal,” says McKenze, who wanted to be a surgeon when she was younger. “I wish I could go back to how it used to be. I want to be a normal teenage girl.”

In some ways, she’s still a typical teen. She loves all things Harry Potter and Twilight, and posts videos on her YouTube channel about what it’s like to live with these conditions.

“I want people to realize that living with chronic illness isn’t just hospitals and all of that,” she says. “You’re also going through stuff at home as well.”

When McKenze does leave her house, she has her 2-year-old service dog and companion Makki, a Goldendoodle she got in 2016, with her. Makki is able to sense if McKenze is going to have a reaction about 20 minutes before it happens and warns her by licking her fingers — signaling McKenze that she needs to take medication to ward off the attack.

“Before I got her, I was going to the emergency room weekly. Now I have a lot more freedom and haven’t had to use an EpiPen in a while,” she says.

For McKenze’s mom Angie and her stepdad Jeff, watching her go through this has been excruciating.

“We just want her to live her life,” says Angie, 42, who works in health and wellness. “We do what we can — and we just don’t schedule anything. We literally just go with the flow; some days we don’t do anything, some days we’re able to get out.”

McKenze knows that she not alone. Along with Jeff and Angie, she has her sister Halle, 20, and brother Logan, 12. The family relishes the moments when she’s feeling well enough to do things, and sometimes goes to play mini golf.

“I never imagined my life would be like this,” she says. “I’ll always be sick, but now I know how to live with it.”

They also created a GoFundMe page to help with medical bills and travel costs.

For more from the exclusive interview with McKenze, pick up this week’s issue, on newsstands Friday.