Is my baby not full?

Hi, i am a first time mom of 5 week baby boy. My baby wqs born tongue tied and got the release when he was 3 weeks old. I have been practicing breast feeding with him ever since and his latch has been great after the release. But he is all the time fussy and not sleeping much now that he is 5 weeks old. I have been reading that he may be in his cluster feeding time. But i am sitting with him for hours and he is latched on to me. My LC told me that you will always have milk for your baby. But it is really discouraging to see him asking for milk qll the time and I am not sure if I am doing enough. I want to exclusively breastfeed him but I am having to top up with formula sometimes. And he does drink the formula as well. Has this happened to anyone and can someone help me?