I work pretty much every day. Most nights too. I tried to solve this by asking my boss to take on a new member of staff. He agreed. At the time my sister was desperate for a job but was struggling to find work that would fit around her partners shifts for childcare, so I put her forward for the job and agreed to cover her shifts when he was working.
Instead of ending up with less hours, I have more. She was on holiday last week. I covered her shifts. Her DP is working this week so I am covering her shifts. He is off next week and lo and behold they're going away again
. I will be covering her shifts.
I won't see my children at all over the holidays at this rate 
I told DH I plan on a taking the last week of the summer holidays off, unpaid (we don't get paid holidays - don't ask) and would use some of our savings to subsidise my missing wage.
We can afford it. He would rather use the money to pay off debts that are under control i.e. we are meeting the monthly payments without having to go without anything.
We have a week away booked, which I have off and will be going camping with the kids, but I want more. I want to take them places here and do things with them at home. I want to spend more than 1 week out of 7 with my children. That is more important than credit cards and interest rates, surely?