If you suspect tht your boy is teething, you might want to feel his gum to check...and also tht time when my son was teething, we brought him to pediatrician who prescribed a gel for him
I think there is on the shelf gel, but not sure which one.
Btw, does your son recently like to put fingers in the mouth? Tht could be part of sign of teething too.....and like to put things in the mouth
Or you might want to monitor your son for next few days, if continute to be like tht could also be a passing phase
You mention tht your son seem to be sleepy, did he get enough nap time? cos baby if not enough sleep or not enough milk will be cranky.....