Bluebellwould, I do feel for you, but like Kalu, I'm going to sound harsh.
A few months ago my friend messaged me, to say she thought she had bowel cancer and was convinced it was terminal. Her words not mine. She hadn't been near a doctor at that point.
She then pestered her GP (managed to get a face to face appointment each time) who tried to convince her there was nothing wrong with her, as all the tests had come back negative.
She then insisted on an endoscopy and that came back negative. She went back to her GP and demanded an appointment with the coleractal surgeon.
Remember, this is all during a pandemic, when most people (including myself) were having treatment postponed. The surgeon wrote to her and said he had no worries about her, but would arrange an MRI if that would reassure her. It came back negative, nothing untoward.
She then phoned his secretary and demanded to speak to him. She made such a fuss that he organised a colonoscopy.
She eventually got one within a week.
Guess what, they found nothing untoward.
What a waste of everyone's valuable time, she deprived someone who was genuinely ill of treatment, because she had been catastrophising.
However, she did have peace of mind at the end of it all. At the moment you don't have that.
If you don't have the investigation, you will end up making yourself ill with worry any way. Like my friend it may be nothing sinister. However, if you refuse the test, you will never know.
I would hate to have a colonoscopy, but I would have it if need be.
I have had worse procedures than that, without sedation, as I can't have any. You just have to get on with it.
If there is something wrong, your poor family will then have the burden of looking after you, just because you refused help. I couldn't put my family through that.