My Jenna will be going in to see her vet tomorrow for ongoing itching issues. She a little over 3 years old, has had some digestive problems this month and we thought this might be her problem, but I'm finding little brown things at the base of her hair shafts on her neck, chin, tail/anal area, plus some just showed up last night on the outside of her vulva (?). She scratching or nipping herself just about everywhere. I'm concerned about the horror stories I've read about ivermectin and fungal agents (not sure if the itching isn't a bad yeast infection, she's had those before and this all started with ears/facial scratching) and I want to be sure the vet doesn't try to throw too much at her at once.
She's going in for other things too, she's had runny nose/sneezing/coughing (she also reverse sneezes) and I'm concerned about her breathing/heartbeat while at rest. Her heartbeat isn't always regular and she seems to breathe too heavily when laying down sometimes. She also has a strange squeaking noise she makes occasionally that's like hiccups but rapid fire ones...sounds like someone wiping a window with a wet cloth. I posted about this a few days ago, but didn't get a response.
Jenna has also had a reaction to the dental injection (porymorphous?) before so I am leery of medicating her. She also has reactions to chlorhexidine chews and she had amoxicillin for a UTI earlier this year that I'm not sure was agreeing with her by the end of the round.
I'd really appreciate some advice for my baby. We go in at 11 a.m. Alaska time tomorrow. My girl is very uncomfortable and I'm worried because she sleeps on my bed and I also have three house rabbits and three cats that I'm terrified I'm going to have to treat as well. Could we please have some vibes for Jenna and all my assorted furbutts?
If it turns out to be mites, I don't know how we're going to get rid of them properly, as my house has old carpet we can't afford to replace and the clutter here is probably harboring dozens of the little nasties. Ugh...my flesh is crawling just thinking of it.

Please, please help...I am sick with worry over all this. Thank you for reading.