2 days after his immunisations and Harrison's temp has gone down but he's still finding it hard to…

2 days after his immunisations and Harrison's temp has gone down but he's still finding it hard to drink his bottles. He'll take his whole bottle in the morning with a bit of an effort but during the day it's a struggle to get even 2oz into him. He just seems to chew on the sides of his bottle. Could his tummy be sore because of the immunisations?