Hi
There are definite links between diabetes and depression, but with such a recent diagnosis, I would suggest that what you are experiencing is very real, and making you very miserable, but it may be more the shock of diagnosis and the adjustment period that we all go through, than the onset of a deep depression. It is kind of like mourning. There are some articles on the internet about the different stages of grief that you may find interesting, if you have a google.
Basically we go through the grieving process when we are given the diagnosis, and for me, knowing what was happening gave me more confidence to roll with the punches. Knowing that it is 'just a stage' and 'this too will pass', is deeply reassuring.
I can't advise you on whether to go back to work or not. We are all different, and we each have different circumstances. But for me, the worst thing I can do when I feel down is to sit at home and be inactive. If I am busy - whether that is work, or going out, or shopping, or DIY, or any one of a 100 things (even reading the forum and finding out about diabetes), then the better I am able to handle the situation.