Hi DavyG,
regarding your main question about feeling tiered after eating and being able to sleep for hours after food. I have a similar problem I feel fatigued virtually all the time. It did improve slightly when they increased my metformin, but I've always put it down to my depression and something I have learnt is that diabetes can go hand in hand with depression. However, another possibility is sleep apnoea or thyroid problems. If I was you I'd make an appointment with your GP and get checked out as it might not be the diabetes where you sleep so much. I'm not saying you have any of these things merely that it might be something else other than the diabetes going on.
Hope you get sorted soon.
Take care Maggie