Hi OP, I am so sorry to hear you are suffering with health anxiety. I have suffered with it my whole life. I can remember as far back as 9 years old, when my breasts were growing and I thought the pain meant I had breast cancer.
As I’ve gotten older, it has significantly reduced and even more so when I had children. I also had to face my fear of cancer head on, when my dad was diagnosed with a terminal brain tumour. It made me realise what it is like for someone to be genuinely unwell. It became so clear that all of my symptoms were just in my head.
When I feel a bout of anxiety coming on, I will usually try to do an activity or go outside to take my mind off things (sounds simple but it’s effective). I find if I sit around, then my mind wanders. You can also find some meditations online, specifically to ease health anxiety. Affirmations also help, for example, consciously reminding yourself it is the power of your mind and nothing more.
DO NOT, I repeat, do not google your symptoms. I am guilty of this and it never ends well, just fuels the anxiety.
I also make a list of all of the symptoms and possible diseases I believe I have had in the past. When I look back at the list, it almost makes me laugh because I would definitely be dead by now if I actually had any of those things! Brain tumours, diseases, STIs etc. and not one of those fears was actually true!
It is very hard to unlearn the mechanisms behind health anxiety but it is definitely possible. If you are really struggling day to day, I would recommend seeking therapy as well.