Congrats on your pgy!
Have you read the sticky at the top of this folder? It answers quite a few of the questions you asked in your OP.
Info. on Vitamin B6 is in a sticky in the first tri folder, I think it is up to 150mg daily. Long term high doses are not safe but as far as I'm aware, you are not in that league at 80mg daily.
Ondansetron (Zofran) is available and yes, it does tend to be a Consultant only prescribed drug and not all consultants will prescribe it. Some are happier to write a script than others. Mine was not too happy about prescribing it to me and although I did have quite a bit as an inpatient, the medical team I was under preferred me to have steroids as an alternative when I was out of hospital (which was hardly ever in the first tri lol). I used them in addition to 8 other meds during the second tri before I found the correct combination for me. I must say, the Ondansetron was fantastic but the steroids were good too. Just not quite as good. And remember, you may need a combination of drugs / doses before you find something that works for you.
Preemptive treatment has been shown to have a beneficial effect so if I were you, I would go back to your GP and get a prescription for something - one of the first line meds to start with or maybe a combination.
As you fall in between the cracks of not been admitted but not seen the mw yet either, your first port of call is your GP who can get you admitted to hospital should you need it or via A & E if it is out of hours and you're desperate. Let's hope you don't get that bad!
Congrats again, GL and keep us posted