Need BF encouragement

I am an EBF FTM. My son is almost 3 weeks old. breastfeeding has been going well until the last few days. My son goes through some cluster feed periods and I am convinced these are due to my supply not being enough to satisfy him sometimes. I pump after feeding him occasionally and I am thinking I should start doing this after every feeding. I think he is not getting enough bc when he cluster feeds and gets very fussy, if I offer a bottle of pumped milk, he chugs it and is perfectly happy for 3-4 hours. He does not seem to have any confusion or preference for breast versus bottle as far as I can tell. Maybe it is just hormones, but I am feeling terrible - like despite trying my best I cannot provide what my baby needs. I really appreciate any advice or words of encouragement  more experienced moms may have.