LO rejecting milk and not finishing entire bottle

hi mummies, my LO is 5mo and i’ve noticed he has been rejecting his milk for a couple of days now and its very frustrating and i worry that he’ll become dehydrated. previously, he would drink 150ml fully every 2-3hrs but now he would just drink around 50-100ml every 4-5 sometimes 6hrs. i’ve tried changing his bottle teat but it doesnt seem to be the issue— he would just choke and cough on the fast flow of the milk. #advicepls