Breastfeeding question

So I'm 5 days PP and I was trying to exclusively breast feed but last night and once today I've had to supplement with formula because it's like I was just empty and my little girl was super frustrated and still really hungry. I supplemented the formula with a lactation aid so she was still on the breast to increase my supply. Does anyone else have a time of day where they feel less full? I feed her every 2 hours both breasts for a minimum of 15 minutes each. She is a sleepy eater so I have to wake her up a couple times while at the boob. I dont know I'm just puzzled. I dont mind supplementing with formula because obviously she needs it but it's obviously easier to just have to give her the boob :p

Also her next feed after supplementing it's like my supply fixes its self and she doesnt get frustrated and eats fine.