I'm a little worried, my baby is 5 weeks old and he has been taking very short feedings for two days, he sticks to my breast for no more than 7 minutes and falls asleep, sometimes he gives me back a little and after two hours he gets up again, sometimes at an hour and a half. I have tried to wake him up to continue his taking but he doesn't want to. Is this bad? Should I give him a formula?