Hi there,
so sorry you are going through these struggles. We all feel tired and a little challenged during that time. Sending you good vibes.
With LOs that are overtired, I found it useful with my DS to catch 1 good nap (like when you are out shopping) and start a routine then. Because you are right, you need to guide your baby into a nap.You can do this by creating a wind down routine and route him to a good timing.
1. At this time he will be more and more distracted by environment, try closing curtains, shades, holding him for 5-10 in silence in a chair. You can sing a little, but few minutes in the dark in silence can help before you put him down.
2. It would be helpful to see your whole routine in an EASY format:
8:00 WU
8:15 bottle or breast? How many oz?
9:30-10:00 nap
It sounds like he doesn't have any feeding problems. It's more like of a distraction problem I think.
Have you tried adding 15 min to his A time?
After 20min nap, do you come in to resettle?