3.5 month old not drinking nearly half has what he used to. Please advise

A sudden change in the last two weeks by little one used to nurse every 2-2.5 hrs and had no issues breastfeeding him. In the last two weeks, he's not showing interest in nursing and I am offering when he goes to sleep, wake up times. I have tried to feed in the dark, low stimulation. He's waking up constantly from naps, waking up multiple times at night and is always tired/sleepy. Hard to get through wake windows. What should I do? He also doesn't take a bottle and we are working with a lc on that to help but I'm all over the place trying to figure out how my baby who ate really well and I had no issues with is suddenly no longer wanting to nurse. If he does then he wakes up at night multiple times to eat. I feed him but before he was just waking up once or twice and eating well during the day. Now everything has gone down the drain.