Hello Simon,
Yes, the trigger could be stress. It could also be subconcious. I think, after I lost my mum, even now still, I am often thinking and talking about something else with someone, but am also still thinking about mum and losing her at the back of my mind. It's ever present in your thoughts, especially in the early days, so whilst you are doing one thing on the surface, you are thinking about something else inside.
Also, if all this happened only last year, it is still early days yet for you to try to come to terms with it all. It all takes a very long time and you never really get used to it. I still think of my dad and miss him every day and he died in 1985.
It could be something as simple as posture or that you need a new bed! I suffer from a bad back from time to time and found out when I was being treated for that, that my bed was too soft and did not support my back properly and that was partly causing it. Consequently, I was getting pain in my lower back and hips and my neck and shoulders, as I also needed to use fewer pillows to keep the spine straight. I was also told I needed to sit with my back straight at work and that can affect the comfort of the front of your body as well as the back, so it might be worth looking at these things too.
I know there is a waiting list for counselling, so I do hope you hear from them soon. In the meantime, try keeping a journal and of course, keep talking to us and to any friends willing to spend time listening. It does help to talk and to write things down.
Wishing you all the best, Simon.