I don't normally post really on this thread but i do lurk regularly

and just wanted to say I'm really sorry to hear you're struggling DW

I remember nights like you're having with my daughter and only last night i was crying over the exact same thing to my husband at 4 am. A couple of things I've found have helped are
1) the Aussie Swaddle for stopping Jack getting out of his swaddle. There's a video on you tube which shows you how to do it.
2) Bringing jack into bed with us on nights he just won't settle or having my oh sit up with him for a couple of hours to let Jack and i get some catch up sleep (though sounds like the latter might not be an option for you? ). I find that if he gets overtired cos of rubbish naps in the day or if he's up too long before bedtime then we'll have a feeding session in the night which never ends cos J won't settle back to bed afterwards. Then the fact he's been up so long makes it worse and we're in a vicious cycle. I swore I'd never do it, but bringing J into bed for a lying down feed and letting us both drop off is our only way out of it. I'm planning on sleep training at 2-3 months but you can't teach bad habits before then and i make sure there are no covers by J, and my arm is round him to stop me or my husband rolling near him. It's only for a few weeks and i firmly believe in doing what works for you and fixing it later if need be! Just as long as you don't let it go on longer than you feel comfortable. I know co-sleeping is against sids advice too so it's obviously a very personal choice but thought I'd share what works for us
3) With my daughter giving a bottle at bedtime or at the 10pm feed really helped cos i was exhausted by that point and my supply was suffering, my let down reflex wasn't happening cos I was stressed and tired etc. I gave a bottle of EBM at first and then switched to formula for that one feed and it did help loads just to give me a chance to recharge. My HV at the time suggested it.
Anyway, hope that doesn't come across as preachy or anything. I just could relate so much to how you're feeling and wanted to share what had worked for us
Good luck and look after yourself! X