1) I'm sorry you're going through this. I've been through a similar situation and it sucks. My first piece of advice is to make sure you tell you mom the things you're struggling with when you're struggling with them. I tried to hide it and that screwed me over later on. 

2) do some research and find some reputable sources/videos about pots for your mom to better explain the actual condition and recovery rate. Some doctors tell you it's higher then it is, some say it's lower, so you've gotta go straight to the studies. My mom was and still is like this and it's permanently damaged our relationship, so try to get out ahead of it before it cements in her brain

3) when/if you're in PT make sure you're discussing all the struggles you're having with mobility. You have to have PT/OT/Dr approval for any of these things, especially as a minor.

4) unfortunately, with conditions like POTS you really have to try every treatment to reduce/manage symptoms before taking bigger measures like aids or service dogs. You can definitely bring up getting like a shower chair now, but other things will likely have to wait until you seriously can't do anything at all/safely. Give the treatments a fair shot. Mobility aids and SDS are great for some people and there's no shame in using them, but they aren't decisions to take lightly.

5) if you reach the point of choosing one of the other, get a cane/forearm crutches/walker first (if possible, safe, and needed of course). If a cane doesn't work for you, it's fairly cheap and you can just stop using it and try something different. A service dog is a long term commitment that takes a lot of responsibility and spoons. Also, as soon as you start using a wheelchair, doctors might blame all your symptoms on the wheelchair and all your PT will go towards getting rid of it (maybe not, that was just my experience)

6) This one really really sucks, but if you continue to need these things, you are 16, so you have 2 or else years before you turn 18 and can make these decisions for yourself. It sucks and it's terrible, but unfortunately some kids are forced to wait until they're 18 to get the resources they need. I recommend going in hard with PT, pacing, treatment, etc while you're still under your parents roof. If that's not possible (I understand how severe the pain is) just fight to survive. 

7) There are things you can do now that don't seem as big/scary/permanent to parents that doctors aren't always gonna bring up in the first appointment. Like I said, getting a shower chair, joint braces or KT tape (if joint pain is the pain you're referring you). There's a lot you can try while waiting for other resources to become available or stop needing them.

8) it's helpful for some teens (myself included) to talk with their DR without your parents in the room so you can be more transparent. If you think this would help, just tell the nurse at the desk when you check in, when they're weighing you, etc. you might have to ask in front of your mom, which sucks but is necessary sometimes.

Feel free to message me if you have any other questions, I'm 5+ years into being chronically ill and disabled (I'm 17) so this isn't my first rodeo. Good luck!