My 3 1/2 month olds milk quantity has dropped by 70/100 ml a day. Also he doesn't take big feeds like before now a days.. Is it normal?

Maybe you can check if your baby started teething. Your baby might be uncomfortable to drink more now, but still enough for the day. Yes please check if your baby's diaper is still wet, need to have lots of wet nappies to be sure he or she is having enough for the day. My boy started teething as early as 3 months, so it was havoc. Want to drink, at the same time don't want to drink. Feel your baby's gums might have potential teeth gonna cut through soon.