Hi LordOfTheFlies,
I'm not a physician so the following is just what I understand of sex hormones and might not be accurate. If your Oestrogen (Oes), Luteinising hormone (LH) and Follicle-stimulating hormone (FSH) levels are high, ovulation may still occur which might explain why you're still getting a period.
Is your treating physician tracking those and have you shared this information with them? If not, it would likely be a good idea to let them know. There are options that may aid in stopping your period for the meantime as well, like a Depo Provera injection. It doesn't help everyone though, as some still experience a period, so it's something to look into should you consider it. It wouldn't solve the root cause, but it might aid in managing related dysphoria.
I'm nine months on T and my Oestrogen level is still high for the average male range for my age. My LH and FSH isn't fully suppressed yet either, so my doctor is keeping and eye on those levels as my HRT continues. I've been masculinising at a steady rate though, so it might not be much of an assurance to read.
I hope you are able to experience the changes you are looking for sooner rather than later. All the best!