The 31-year-old singer calls Shelton, 38, "the happiest person I know. Literally, everything is the best about being married."
Admitting she's "not sunshine and roses," Lambert says: "I'm always anxious. I worry myself into oblivion. I was trying to make everything regimented, and it caused too much stress. I learned everything doesn't have to be perfect. That sometimes it's OK to say, 'I don't want to be the boss today. I have PMS. Bother someone else.' I like things better flawed anyway."
The beloved country singers have been married since the spring of 2011
Six years after making sparks onstage at a CMT concert, the country music power couple wed in May 2011. That year Shelton debuted opposite Adam Levine as a judge on the smash NBC singing contest The Voice, on which Lambert has appeared as a mentor.
The Oklahoma native recently shed 20 pounds, her physical transformation spawning hundreds of headlines.
The happy, stylish couple were all smiles at the Grammy Awards
"When you have to walk out there in front of thousands of people, it does feel good to know your (body's) not jiggling," she reveals. "I'm just like anybody else, insecure and scared of looking bad or being criticized. But everyone's making this big, giant thing about it. It's way too much focus on women's bikini photos, and I hate it. Why do we care? I want women to love themselves whatever they've got going on."
Lambert's January Marie Claire cover hits newsstands January 16.
Blake and Miranda pose together on the red carpet of the ACM Awards