7 month old keeps losing weight. help!

Gabrielle
Hello. My 7mo old son keeps falling on the charts and is now under 2% for weight. He was born 8lbs. So it's not like he started out small. Problem is that he has a small appetite and snacks more than eats big meals. I exclusively breastfed for 6 months. But now he is getting some formula and solids. I've weighed him before eating and he takes 2oz from me but will drink a 4 oz bottle. Problem is he eats every 2.5-3 hrs. (Even throughout the night). He started daycare this month and isn't eating a 4 oz bottle every 2-3.5 hours as I thought he would. he will only eat 2 bottles in a 10 window with solids in between. 
How can I get him to start taking in more for each meal or eating the larger amount more often?  I was thinking of sending 3-3 oz bottles instead of trying to give him 4 oz bottles because right now he will only drink 2 of the 4 oz bottles. 
Any advice or similar situations?