hand munching

Lo
Hi all 
My son was 8 weeks on Saturday. He takes 4-5oz feeds 5 times a day, goes 7-8hrs between his last feed at night and first in the morning. He has reflux and is on Zantac for this which has been a great improvement. But recently he has been chewing on his fist immediately after a feed and I don't think it is through hunger as it's a battle to get him to finish his 5oz bottle most times. He is also quite drooly at times - is he teething?!