My about to turn 3 month old now has started crying when he wants to sleep!?

He used to just doze off, now he rubs his eyes and starts squirming around as if he is trying to fight with his sleep, he cries and sometimes yells, I always think he is hungry but I feed him and he just gets even more upset, until finally I rock him and pat his back until he is asleep! Any ideas on how to make him just go to sleep again or at least why the change??!!