Depression is awful and as it's one of those hidden illnesses you look "ok" to the outside world. I've suffered with it on and off for probably 15yrs+. It's all the little things added up that add to the stress/anxiety and feelings of hopelessness sometimes, although it can be a major life event.
I'm currently on citalopram which I've been taking for a year. I've also completed some CBT courses (Cognitive Behavioural Therapy). I was sceptical of doing these at first but have to say they were very useful and helped.
I'm sure I've read somewhere on here that diabetes and depression are linked
It may be worth checking at your doctors surgery if there are any CBT courses locally. You don't have to be referred by your doctor (well, not where I live anyway) and I self referred myself online.
Hang in there - there is a light at the end of the tunnel!