Testing out medication for a suspected diagnosis without doing the test? Experiences?

Hi! I have several chronic illnesses confirmed, and currently suspect MCAS and gastroparesis based on symptoms (I have IBS diagnosis, but it was based on symptoms only, no differential testing or anything). MCAS is just something I saw when looking up various symptoms (and like, if it's something medically relevant at all, because I have no idea of what's normal anymore lol), and gastroparesis is something that an osteopath I saw a couple times kind of mentioned, but obviously couldn't diagnose herself Where I live, blood tests are expensive as HELL (like, about one hundred $ for a normal one, several hundred for a more extensive one), whereas medications are pretty cheap, so I am thinking of going to an internist and request to try out medication as a way of diagnosis (or ruling out the condition), as that would be MUCH more affordable. It would be medically supervised, but I know that this is an unorthodox method, so I was wondering if anyone has experiences with something like this? I just want any relief for my symptoms really 😭 I'd really prefer to just get an extensive blood test, but it's just not doable financially right now 🥲