Have you tried upright my son has been like this and it due to ear infection and glue ear. Sometimes the only way I can get him to sleep is on me with his head on my shoulder
We had this for about 2 months and after trying many things I realiser he just needed longer wake windows. I noticed my son does well with 7 hours, so we changed the nap and bedtime later to get to that. Bedtime is 9pm atm and he goes to bed on his own again
Sorry no advice but we are the exact same, so following for any advice!