A major goal of scientific experiments and statistical methods is to approximate as best possible the counterfactual state of the world.  For example, one could run an experiment on identical twins who were known to consistently get the same grades on their tests. One twin is sent to study for six hours while the other is sent to the amusement park. If their test scores suddenly diverged by a large degree, this would be strong evidence that studying (or going to the amusement park) had a causal effect on test scores. In this case, correlation between studying and test scores would almost certainly imply causation.
You should contact your Gp…. If your Gp does not do anything then find a better one. Good luck with it all.
The problem with the Internet and worrying is that though there are Plenty of pages with correct information there are so many with false information and also 99% of the time show you something that sounds scary. So my suggestion would be genuinely to avoid looking up symptoms etc on the Internet. I do occasionally but that is if something is on my mind and I would be seeing a gp/hospital doctor anyway within the week.