I'm so sorry about your son. That sounds traumatising.
Yes iv had the pinching feeling. Always my right too weirdly.. it always flares up when my anxiety is in overdrive. Always convince myself it's a cyst. Always nothing. Had a scan for something else and all healthy. It's sometimes right in my hip or right by my hip bone or the top of my pelvis.
Appendicitis .. you would know it's appendicitis. My ex had it and he went from a mild ache to being doubled over in an hour.
Any of the cancers usually come with more symptoms than pain. Also the fact it's on and off means it may be hormone related. But you know this already.
The mind is a powerful thing. Having just thought about the pinching I get ... Iv just had a twinge on my right side
Its absolutely can be from stress and anxiety but if it is persistent and worrying you then reach out to your GP xx