Is this separation anxiety coming out? Like do you think he might be mad that you went away so he's "punishing" you when you come back (by asking for a hug then telling you he doesn't want one). Have you explained why you work and where you are when you work and when you'll be back etc.? How is he when you drop him off? Also does he have a lot of alternative carers or just his grandparents? He sounds like he's acting out rejecting you, which to me indicates he's feeling rejected for some reason. Did you just begin to go back to work? Transitions can be hard and shaky for everyone involved, and sometimes extra explanation/reassurance is needed to get littlies through.

It can be so hard balancing work and childcare, but i think many kids do better with one other carer than lots, as they can feel more secure that, ok, mummy will go to work, then i will go to spend the time with X, rather than not being sure who it will be that day, kwim?

Most of all remember that you're working for his benefit, and him reacting like this is NOT your fault. It's so painful when they reject you, but if he didn't trust you he wouldn't be able to say it to you, kwim? It feels safe to yell at and reject mummy because he knows even in the middle of a melt-down if he asks for a hug you'll give one. He knows you love him. That's the most important thing.

You could also begin a post-collection routine - it doesn't have to be a treat, it could be a trip to the library, a walk in the park, whatever. But then before you go in the morning you can say "OK honey, remember we'll be going to do X when mummy finishes work, so you think about what you want to do when we're there" and he'll have a focus in his day that's beyond mummy coming back.

I hope something in there might help. Anyway, hang in there, you're doing a great job.

Bec