jessieblue, I'm sooo sorry you're going through this. I also get health anxiety and end up in a complete mess. For me, there are elements of 'reality' in there and then there are things I just freak out about because I am ultra-focussed on my body.
It is hard to know when to get the tests done (in case those can reassure you and you can move on) and when to resist the urge to keep investigating because of 'health anxiety'.
There is a test you can have run on your poo, which checks for blood in it - faecal occult blood test (or something). You just collect some of your poop at home and submit it. You probably want to make sure you are not bleeding from your fissure or piles at the time (both of which I get intermittently too, BTW!). If that comes back negative, it might reassure you?
I have been so anxious about my health in the past, when I went through what I now refer to as 'the endo mess'. I was anxious about my endo symptoms but then I seemed to get all these other symptoms which were nothing to do with endo - night sweats, heart palpitations, lower back pain - I even worried I felt something in my breast. I just couldn't shake the feeling there was something wrong and I needed to find it. I think for me, it was because my endo didn't show up on scans or tests (as it often doesn't) and it wasn't just when I had my period, I also had weird pains throughout the month. So I got myself in a mess that there was some other undiagnosed thing wrong with me and it wasn't endo... Part of the reason I had my lap surgery for endo was really just so someone could take a look and I could get on with my life and stop looking for something else.
The thing is, I was so anxious at the time I would wake like someone had injected me with adrenaline in the morning - this shot of pure cortisol. My poop was often sloppy and runny just from the stress and food just went right through me. I was losing weight even though I was eating ridiculous amounts - I mean - I would go to Gourmet Burger Kitchen and eat a massive burger and chips, and a chocolate milk shake - and I would lose weight!!! Of course 'unexplained weight loss' is also a symptom of terrifying things, so the fact I was losing weight only freaked me out even more. It was an awful time for me, so I really feel for you.
I had ECGs for the heart palps (this was 8 years ago); I had a rectal MRI and a flexi-sigmoidoscopy; endless bloods; ultrasound on my breast at the breast clinic; MRI on my lower back; endless chiros and osteopaths - but for me, it was just that I knew there was something wrong and no scans or tests could find the cause of it... until I had my laparoscopy. When I had the lap and they found endo, I was just so relieved that I had an explanation and as I recovered from surgery, I felt my anxiety dissipating as well and the whole awful time passed. I kinda knew 'I am having this surgery not because of unbearable pain [because it never was unbearable] but to get a diagnosis and move on'. Which sometimes felt a bit OTT, but I had to do it.
One thing I have found which really helps, is this app you can download from the app store called 'Curable'. There is loads you can access for free on it, and I then paid to access all of it because it was so useful.