Temp needs to come up...get him inside under a towel or blanket tent and warmthe air with a blow dryer..or put the baby in a plastic bag, head out and sit in very warm tub of water..
Could be floppy kid Syndrom or too much milk..either way....No milk for 12-24 hours feed electrolytes from a bottle ..
I would give thiamine (b1) or fortified B complex
electrolite recipe as follows.
Homemade Electrolytes
A half gallon of hot water
2-6 Tablespoons of Unsulphured Blackstrap Molasses or any moslaases she has onhand or honey
1-2 Tablespoons of Either Sea Salt, Epsom Salt, Baking Soda or Table Salt. (choose Baking soda to help off set the acidosis of FKS)
1 cup of Apple Cider Vinegar
Mix well and drench or let them drink it.
Feed this with a bottle at the follow rate
Weight baby..multiply that weight by 16 to get weight in oz, multiply that by 10% to see howm uch fluid he needs per day, divide that into 4 feedings..
BUT GET HIS TEMP UP FIRST and a thiamine or fortified B shot..