Breastfeeding/weight gain

My son is 8 weeks old. He had trouble gaining weight during the first month. Took him a month to go over his birth weight. He is pooping and peeing and eating every hour and half sometimes 2. I’m exclusively breastfeeding. Should his weight gain be this slow or is there a problem with my milk. I’m being forced by family to supplement with formula but I’m really hesitant. I want to continue breastfeeding. What can I do to help baby gain weight faster. At my last appt Doctor was happy with baby’s growth.