I think the shock of moving from the free and easy world of Reception into the (sometimes) much more formal and structured world of Y1 can be a huge shock to some children.
If hunger makes hime more irritable, are you able to feed him a little tea as soon as he gets in from school? I do this with my 3DSs and it really helps. They have maybe a boiled egg and soldiers or some pancakes with banana and honey. They then relax (play, draw, watch TV) until their 'proper' tea is ready.
I don't worry at all about homework at this age...if they are doing what they should at school, there is no need to do more at home, IMO. I usually hear them read at breakfast when they are more 'with it'!
If any one of mine is showing symptoms of extreem tiredness, they have lots more snuggles and cuddles and a nice early night (given as a treat, not a punishment, so often tucked up in my bed with a story tape!)
I hope your DS is soon feeling better. Meanwhile, do remember that the tantrums are a way of communicating with you. He may not know what he needs, but if you manage to find out and meet those needs, his behaviour will improve!