Could you start to future plan now? Even though you can't make many immediate changes with a newborn, just being proactive and making plans for the future - even if they're just while you're sitting on the sofa with a notebook and feel like pipe dreams at the moment.
Look at doing a degree through the Open University. Look at doing an A Level at college one evening a week - just to get yourself back into the swing of things and so you have the confidence of recent learning.
I went to university when my first was a toddler and came out with a first. I did a diploma through the OU when I was on maternity leave with my second to 'keep me busy' and started my Masters when she was 1. So it is possible.
You can do it part time and take 6 years to do your degree.
That would give you time to work out what career you wanted to do at the end of it and your youngest would be well into full time school when you graduated.
I'm a single parent and did most of the above as a single parent so it should be manageable with a husband - they are his children too, after all!
The first thing I did, was create a 'mind map' and a pen portrait of Me - who I was; who I had been before children and who I wanted to be in the future. And I used this to be more 'mindful' about who I was and how I lived my life.
I colour coded it and organised things into:
What can be acheived immediately with little effort (short term goals) - e.g. a bit of self care - maintaining my nails again; spending time in nature again.
Things that would take a bit of planning (medium term goals) - e.g. losing 2 stones; taking up swimming again.
Things that would be longer term goals that required something else to be achieved first (long term goals) - e.g. changing career; saving to completely overhaul my wardrobe once the weight was lost.
I found that once I started to view myself as Me again and not just "ex wife"; "mother" etc, things really started to fall into place. I gained in confidence and ended up doing things for myself that I'd previously only dreamt of - I now play bass in a band and gig most weekends now that my children are old enough to be left for an evening.
You are so young and this is your life. You have 5 amazing children. You have as much right to live it to the full as anyone else.