Help! Struggling to gain weight

My son is 3 weeks old. When we were discharged from the hospital, he had dropped 10% down from his birth weight. I am trying to exclusively breastfeed, but he is struggling to gain weight. When he was born, he weighed 6lbs 14oz. We can’t seem to get him past 6lbs 8oz. Most days he is between 6.6 and 6.8. Any other mamas go through this? I really want to exclusively breastfeed as long as I can! But everyone in my life is pushing me to use bottles and formula. Help plz!!