Hi Mazzy, It's hard not to feel down but then with diabetes it's a case of take each day at a time.
I can only speak from what i've learnt about being diagnosed with type 1 and where i've come so far in the last year, I have read Dr Bernsteins book about diabetes and diet and exercise. I have had huge swings in mood and these are down to swings in my sugar levels, the more up and down i am the harder it is to stay on top of it. Diet has changed this, I eat low carb, so just cut out all bakery, potato, pasta (i.e. fast acting carbs) these send my levels sky rocketing, also means I have to take more insulin which then can lead to hypos if i've not properly calculated it, exercise is really important and walking is perfect, keep on doing this.
Get yourself checked into the doctors and talk about your energy levels and poorly tum, they should be able to work out why this is, anxiety and depression are most likely linked to this but you need confirmation from a professional and most importantly try and get onto an expert diabetes course, your DSN should help here, they are good for knowledge and support.
When I feel down I always think there's someone much worse off than me and i'm alive, so that's a bonus, good luck x