You can run medical, scientific experiments on yourself.
In fact, you should.
I’ve never been lab tested for gluten or lactose intolerance, for example.
But I have tested myself via the removal and addition of gluten and lactose, controlling against other factors, and noting the results.
Those foods do not work well for my body, at all. When I do eat them, I feel like crap.
This is something they didn’t teach you in school: that you have the power to figure out what works for you.
Yes, you should follow a process when doing this. Keep a log of everything you eat, and how you feel, for a week. Then remove one ingredient, for a set period of time. (For gluten, I recommend 30 days.) Continue the log.
It’s slow and laborious, but the process of removal is a legitimate test.
You don’t need to see, or pay, a doctor for that.
Save those visits for when you really need them.