I've never experienced this, to be honest. I have had
DD1, falling over for no apparent reason, taken very seriously by the GP and fast-tracked to hospital, kept in overnight then seen by a Paed consultant, who asked a colleague to see her, then passed on her care to a third Consultant who had a special interest in neurodisability. Whole host of tests done, and more scheduled, taken very seriously, later diagnosed with a brain malformation.
DD2, severe reflux, went to GP, who referred on spot to hospital, seen and given reflux meds, went back and asked for specific meds, given without question.
DD3, ok so far.
I do wonder if it is because I am a RGN, so they talk to me on a professional level, or if it is just that I live in a good area. I do have friends/relatives from the area that say what you say though, so perhaps it is my RGN status that swings it.
All I can suggest is play the game. Keep a diary, so that you can be very specific. Say "I gave DC this at this time, and by this time, he was in discomfort. I gave DC this at this time, and by this time he had a rash," or whatever.
I am about to keep a diary for DD1, because her weaning a medication is coinciding with flooding her bed through a pull-up. Coincidence? Possibly, but I think it is too neat for that.