Advice for advocating for my needs? - disability/chronic illness

I feel like I need to invest in a rollator/walker however whenever I've talked to my current doctor about similar request they scoff at me. I don't have any diagnosis that would explain my symptoms so many doctors push my concerns to the side. They tell me the classic "you're too young, plus your results are normal." I also live with a foster family so I don't know how my foster mom would react to the request. 

The rollator I have researched and I want to get also cost hundreds of dollars and accessories, like an umbrella would cost more and I don't have the money. I doubt insurance would cover it because when a doctor did agree a cane would benefit me, the cost wasn't covered because "it was only recommended and not prescribed." 

I am also scared of how my school would react and being judged. I HATE being perceived.

Where I live winter is approaching and I am honestly scared. I don't know how to address this. I couldn't handle Halloween and the snow hasn't fallen yet. What's going to happen to me in the winter? I might also have to walk home!! BY MYSELF!! I can't do that! 

To summarize, I want/need a rollator that is not covered by insurance, I live in a place with really bad winters, and I don't feel like I am getting proper medical support. This scares me and I would like advice because I don't know how to approach this.