You could consider alternating the tylenol (paracetamol) with ibuprofen for a bit more effective pain relief if his teeth are bothering him a lot.
Sounds like he's spirited - DS did better going to sleep for naps when I brought something from his last activity to sort of bridge the transition from playing to going into his cot for a sleep.
Something has to be bothering him.
Digestive issues - Have you started solids? Offered anything new lately? Tried thickening a bottle with rice cereal?
Pain - teeth?
Coming down with an illness?