Sleep or feed?

My 3 month old drink 120-150ml every 3 hours. Sometimes after 2 hours he will crank badly, I am guessing that he is sleepy but my MIL always say he could be hungry. As I don’t want to overfeed him, I will try to make him sleep first. If he does sleep, I will not feed him until he wakes again for another feeding. So if my LO slept, it means he is just tired instead of hungry right? I just don’t want to overfeed him, because each time he cries, my mil will say he is hungry