It sounds really tough OP. No one should be judging you for expressing these most difficult thoughts and feelings. You can’t help your thoughts and feelings. They are what they are. But anyone with an ounce of compassion will know how hard it is, as a parent, to have them. I think it’s honest and healthy to talk about them. With help and support, hopefully you can figure out a way to improve things for all your family’s benefit.
I think the idea of simplifying your life as far as possible is the first step to take. If you can keep your DS calm for more of the time, then this will help create space for other things. Identify the times your DS is happiest and most calm. It might be watching TV, lining up toys, being in a sensory room, going to the local park (some people with autism do enjoy going out). Make these the key things you do for a while.
Then look at other ways to help your child, depending on his particular needs as you understand them. Creating routines (morning, bedtime), visual timetables to show the routines, simple instructional style language, reducing sensory discomfort wherever possible, are a few that might help, off the top of my head.
Look for support wherever you can. Contact social services and ask for a needs assessment for your child and a carer's assessment for yourself. As a child with a disability your DS is a ‘Child in Need’ (different to Child Protection) and you may be able to get some respite provided. As soon as you have baby number 2, contact Homestart. They are a volunteering organisation that may be able to support you. Apply for DLA if you haven't already. This will provide some financial help to enable you to get a cleaner, pay for one of those meal package deliveries occasionally, or whatever else might alleviate the stresses or meet the extra costs of coping with disability within the family.
Once you’ve started to recover your emotional resilience, you can then start thinking about longer term strategies, such as the best educational placement for your DS. There are lots of organisations that can offer free guidance on all matters SEN related, and slowly but surely is the mantra with this.
Take it a day at a time right now OP. Try and let go of expectations of what should be, or what you thought it might be. The truth is, many, many people have difficult and stressful lives, even if the likes of Facebook and Instagram would have you believe otherwise. You are not alone.