Getting enough milk?

My son is 11 weeks old. At first he didn't want to latch at all so I went to pumping and hes been only drinking breastmilk in a bottle. I never stopped trying to latch him and recently he'd been latching on right away with no fuss!! My concern is though, how do I know if he's actually getting enough milk? Should I offer a bottle right after he finishes nursing? I saw a lactation consultant when he was about 3 or 4 weeks old and he latched with a nipple shield there but he was weighed before and after and he had only taken about 1.5 oz of milk in like 20 minutes. Any advice?