20 week old feeding... advice needed πŸ™

My son used to drink 180ml flat.. but the past few days I struggle to get him to drink ... hes bed time bottle tonight he only drank 30ml the night before only 60ml and he slept from 8pm to 4am

During the day (hes at day care) I usually pack 4 bottles but hes only had 2 of them ..

I'm concerned or maybe I'm missing something?? FTM here so any advice/thoughts welcome πŸ™