Don’t ignore pain, listen to it. If it hurt that’s because you need to fix something. So think of what you have done that cause it. Did you change your habit? Why on this side and not the other? Did something different happened, not necessary in sport, but in your life?
Then try to change and see if you fixed the problem.
I don’t have a head torch, but I think I’ll buy a Fenix HM65R-T (or a similar model). I’m particularly interested in the surdiness, and the standard lithium battery.
I active walk the first hundreds of meters (letting the GPS time to warm up) and run easy the first km. At the end, easy last km. That’s it.
Science shows that static stretching before is counter productive. Static stretching at the end depends on you: it can be productive or counter productive. If you feel the need, you can do it, bit if not, nothing wrong to not do it.