I understand exactly how hard this is both as a mum and a childcare educator. I have worked in the childcare field for 21 yrs and there has only ever been one child who we couldnt settle and ended up leaving. Ever other child of various ages have eventually settled in their own time. It does take time, some it takes a few weeks and some a few more weeks. Kids will not eat or sleep very well until they settle this is normal. Do you have time to spend with your son when you drop him off? we usually encourage this at our centre. Take some of his familiar things he likes eg teddy, blanket, dummy etc. We even send home a photo of the main carers in the room to stick on the fridge so you can talk about them to your child when not at daycare, to help them become familiar. Maybe you could ask for a photo.
Give him a little time and yourself to adjust. Try and stay positive and keep persisting good luck