Not eating?

My little boy is almost 4 and a half months, and he’s usually such a happy little guy!

For 2 weeks now he hasn’t been eating properly, 2 minutes here and there (ebf) with one really good feed at night before he goes down. He sleeps through the night but I give him a dream feed when I go up. We’ve struggled with thrush a few times but I’ve been taking Fluconazole for a week, he’s been on darkarin gel, and definitely feel that’s getting better. Why is this happening? He’s normally such a good little eater and loves his milk. I’ve expressed and I’m definitely making enough milk. I’ve tried to give him a bottle, but he struggles to take that too. It’s really getting me down as he is screaming most of the day and I just want to help him, but I don’t know how.