So, for those that responded and didn't feel the need to be rude/mean in their response - thank you.
I started calling twice a day because the nursery suggested it. When I left him the first few times I would call to check on him and then they would say I could call back later on if I like, to see if he was doing any better. He initially cried pretty much from start to finish. And honestly, it just became a habit after that.
Lovely to see that everyone did so well at GCSE maths - used to be one of my favourite subjects at school too. The relevant figure is in fact 6 - there are a maximum of 5 other children in with my son at any given time. Typically, a call would only last two minutes at the very most. So feel free to have fun working out these numbers 
I do probably have some anxiety issues I need to deal with, it has actually been mentioned to me before. I have tried seeking out help and honestly felt really ridiculous wasting people's time because it did not really feel to me like a "real" problem and I know other people have a lot more serious issues out there. But, I have actually decided to try once again to talk to someone about this, so thank you. If nothing else, perhaps this post has perhaps really highlighted to me that I could do with a little help for myself.
As for trusting the nursery, honestly, I don't trust them 100%. We have had a few (albeit small issues) with them, aside from the discrepancies with the daily sheet, so it has made me wary that they are not always paying my son the attention they really should. But he has only just started to settle there and his key worker seems genuinely nice, so I don't want to just pull him out for him to start all over again somewhere else with no guarantee they are any better. Especially as his nursery is the only one in the entire borough with an Outstanding rating from Ofsted (for what it's worth).
And finally, I just wanted to say that I did not call today and the sky didn't fall in 
Apparently he had one of his best days yet and even JD a good go at all his food. Even ate a breakfast, because my husband had forgotten to tell them at drop off we had fed him at home! Now, I know how he does has nothing to do with whether I call or not, but this has made me feel a lot better. The nursery staff did ask my husband if I was ok at pick up though, because they hadn't heard from me and wanted to make sure I was alright 
Ok, essay over and my little one is now awake
so I'm signing off now.
But thank you all and goodnight! 
Well except the meanies - you guys should really take a look at your own lives...find some happiness in it instead of sharing your misery with the rest of us