But with pain so severe it would keep her awake at night - something she tried to put down to hormones and stress - Ms Pay finally went to see a GP.
Even the doctor was not overly concerned and she waited five weeks for a mammogram and ultrasound where they also took an immediate biopsy.
Two days later a locum GP she had never met before dropped a bombshell - she had aggressive stage three breast cancer.
"I just felt like it wasn't happening to me, [thinking] they'd ring me up later to tell me they'd got the wrong person."
Four years on she's now accepted breast cancer is part of her life and stopped wondering if it was caused by something she did, ate or drank.
"I just think it's your journey. If you're going to get it, you're going to get it," she said.
Ms Pay, whose two sons were seven and 10 at the time, fought the disease with chemotherapy, radiation and drug treatments. She also had a single mastectomy followed by a breast reconstruction.
The lymph nodes on one side of her body were removed and she now suffers from lymphoedema - a build-up of fluid in her arm requiring weekly treatment.
Despite a string of complications, a positive attitude, strength and determination paid off and she went into remission.
Sadly, within three years of her initial diagnosis, the cancer was back.
In April 2015 pain in her chest revealed the devastating news that it had spread to her sternum.
After initially feeling pressure to get her affairs in order quickly, she decided not to ask doctors for a prognosis and instead live life to the fullest - however long it may be.
"All through the cancer diagnosis I've been pretty positive. I actually think you live longer if you're positive," she said.
Originally from the United Kingdom she travelled home to the support of her close-knit family and considered returning permanently, before realising New Zealand was now home.
A primary school teacher aide, she made the difficult decision to give up work.
"My children are more important and so is my health," she said.
She now volunteers once a week at recycled clothing shop, Tallulah.
"I like people and I like to be busy," she said.
She also pushes herself physically, taking her dog, Henry, for regular walks at Kaiate Falls.
"I'm still a full-on mum. I still go to all the sports. Nothing's changed there, I want their life to be as normal as possible."
Chances are the cancer will spread somewhere else in her body but that's not something she focuses on.
"I'm grateful that it is only in my sternum," she said.
Ms Pay will have her next scan in three or four months' time which will reveal if the cancer has grown or spread.
There are times the cancer journey is a lonely one as friends fade into the background or struggle to understand what she is going though.
Her message to those who find cancer awkward is simple.
"It's harder living with a secondary diagnosis than it is for someone to come and see me."
She admits cancer has hardened her up a lot.
"I used to be a yes person. I'd say yes to everybody." (Now) I only bother with people that bother with me."
Her happy place is off on adventures in her campervan with sons, George and Charlie, and bulldog, Henry.
"I'm still smiling and I'm still happy so that's the main thing. I don't get miserable very often."
Along with an amazing network of friends, it is support groups and organisations like Sweet Louise, which help her though.
Started by the husband of Louise Perkins, who lived with secondary breast cancer for a decade, the group recently celebrated its 10-year anniversary.
Each year they send women with secondary breast cancer $500 worth of vouchers to use on local services including beauty, home maintenance, florists and movie theatres.
Members also meet regularly with a support co-ordinator and catch up for coffee together.
Ms Pay also receives support and advice from Tauranga Breast Cancer Support Services which will host it's annual fundraising HOT Pink Walk in Tauranga on Wednesday.
This weekend Ms Pay is holidaying in Rotorua with Shocking Pink - a support group for women under 45 who have been diagnosed with breast cancer.
The group gets together once a year, alternating between the North and South Islands, to celebrate life and have a laugh.
Sweet Louise
During October, those wishing to support Sweet Louise can text "Sweet Louise" to 4662 to donate $3. Sweet Louise aims to raise $100,000. This money will be used to provide a range of support services such as two additional regional support workers, 20 members' wigs or 5,000 counselling sessions for members or their immediate families.
