5 week old barely eating ?

My 5 almost 6 week old baby is barely eating her bottle she is formula fed we haven't had a problem until today she normally eats 3 Ozs every 3-4 hours and today she wasn't eating much maybe 2 Ozs if that she spit up almost her whole bottle at one point and she just falls asleep I have had I wake her up a couple times today o and when she does eat it's like she is holding formula in her mouth and just letting it spill out of her mouth so she isn't swallowing much I want to call the doctor but I'm going to give it a little while longer atleast see what happens tonight maybe her belly is upset? I gave her some gripe water for gas starting yesterday and a little earlier today idk if that has anything to do with it? I'm sorry im all over the place it's late.... I'm just looking to hear pols thoughts or has thi happened to anyone before im a new mom and very nervous about everything my boyfriend always tells me to calm down and see what happens but it's not that easy!