So sleep deprived- what am I doing wrong?

I have a 7 month old and his sleep is absolutely terrible.

I feel like such a rubbish mum- no one else seems to be having this issue???

He slept though until the 4 month sleep regression and then we never had a good night again. 3 nights last week he woke up about 4 times and then woke at 5 am and we were celebrating!!

At the moment (and most of the time) he is up every 40 minutes.

I feel like I’ve tried everything, adjusting naps (which are also crap and short- but they improved for a couple weeks then are bad again??)

He’s in his own room and cot, changed his bed clothes and put two thermometers in his room, white noise machine, complete darkness, topping him up for calories in the day etc….

He doesn’t take a dummy. If we let him cry he gets hysterical in minutes so not an option.

He also won’t settle for my partner at all he just wants me to settle him back down every time

Any advice at all is appreciated