Help. Infant spitting up.clear liquid

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My 6 week old is eating significantly less and spitting up clear liquid. He was on 4 oz and was bringup alot after eating. Today he is only eat 1-2 oz per feed and an hour or so later coughing and bringing up significant amounts of clear liquid. He is pace fed. But is not like him to not eat at least 3 oz every 3 hours.