Hi Ana
In ALL your poses see what you can do to lengthen your neck and relax that shoulder away from your ear (both shoulders of course!). Until you see and feel improvement I strongly recommend NOT straightening your arms or clamping them to your head in half moon side bends. I know that is what you are told to do but this pose particularly can really exacerbate problems like yours.
How amenable are the instructors at your studio to modifications? There are things you can do. Firstly simply bend your arms a little, bring the chin up to correct position because in all likelihood you are dropping it a bit, drop the shoulders down and back, and bring the arms back. Back off a bit if your shoulders climb even a little bit.
You will get MUCH more out of this pose if you are not struggling to squeeze your arms and head and causing pain and strain.
Namaste
Gabrielle