Sammy hugs for you. You mentioned that this has been worse since DS hit 4 months. I read a fair bit about sleep regression at this exact time - if you google it you'll find some more information, apparently it is really common. I know you are using gentle methods which I really respect. Would you consider leaving your DS to self settle and grizzle but go straight in as soon as he gets upset? Just a suggestion.

Do you have a swing you can use? Maybe put it in a dark room and use it without the lights/music and hopefully he will self settle it in himself to the point you can nurse him again and put him down.

I am sure there will be others who can give you some much better advice. Good luck