Not necessarily the route to poor-outcomes but say you have the most prestigious job in town, a decent salary with le highest status but you're to living "paycheck to paycheck" and "just getting by".
You're gonna have to be willing to make some adjustments because you have a 2nd child on the way, by choice not by chance.
Now, these adjustments are going to happen whether you like them or not- your life is going to change there's no room for doubt about that.
Whatever your wage in the world, big or small- whereever you live there's no one who'd deny it's going to go a lot further funding a family of 3 (you, gf, child) rather than of 4 (you, gf, child 1, child 2)
So you've already made 2 adjustments , you've got savings and a very necessary second job but as recognised above extra costs come with having 2 children so that means you have 3 options.
Boss, can I have more hours?
1: Here's some some hours mate (these hours conflict with your 2nd job).
Mum, should I apply for a 3rd job?
2: The hours of this 3rd job don't conflict with any other job (unlikely) but you become much more fatigued leading to an injury at work which puts you on sick-pay and your family into the red.
Mum, I like my current job but should I plan to get a better job in order to provide more financial security for my children?
3: Yes. whether that's joining a new trade or going up the ladder in your old one- this will provide less chance of financial insecurity for your children and enables you to not have to work 2 jobs to get by- it also allows you to spend (relatively) more time at home compared to having 3 jobs.
This is the most-sustainable solution, its also the only long-term one.
Mum, should I carry on as normal as if nothing ever happened?
4:You can't carry on as normal, without trying to adapt to the financial circumstances of having 2 children as this will almost certainly lead your young family to financial ruin, possible homelessness and it puts a strain on your marriage
Best option seems to be option 3