I think that J am bipolar?

I’m currently 18 and despite dealing with recognisable bad mental health from the age of 10/11, it was only at 16 when I was diagnosed with Anxiety, as well as Depression. At 17, I was finally diagnosed with ADHD. Even though a diagnosis can at the time make mr feel more understood and supported, overtime I feel like there is something missing and despite these diagnoses, I end up feeling like I’m back to square one because the problems aren’t effectively being dealt with. I am trying to get an assessment without my mum knowing though because it has been difficult for our relationship. She is a paediatrician and neurodevelopmental conditions, particularly regarding children, are her areas of expertise as a doctor. However, it is hard because in our relationship she often approaches me as a patient rather than as her daughter. This causes arguments on who knows better and what is best for me. Also because I’m African (Nigerian), there is often a taboo with mental health in our community and I recognise my mum upholding that behaviour in our conversations. She has helped me get the diagnoses that I have now, by trying to speak to her colleagues to get someone to see me, but I really had to push her to see how much I was hurting before she really took initiative and also because of my upbringing I had to hide or make excuses for my pain and trauma for years before actually cracking. The diagnoses that I have collectively, I believe, an impact or play a role in what I think is undiagnosed bipolar disorder. The impulsive and manic behaviour and episodes in my ADHD and my heavy depressive periods from my depression. My sister (23f), who is currently in graduate medical school, says she has recognised these patterns of behaviours in me for years and said to me that she thought before I had my ADHD diagnosis, that I was possibly bipolar. She still thinks that it is possible that I am and only when I opened the conversation to her, she told me because she didn’t want to assume that I was and offend me. Also my close friend (18f) who has known me since I was 11, described the same concern as my sister but held back from telling me until I opened up about it being a concern, as to not offend me and she said that she’s not a medical professional and didn’t want to assume. Multiple friends have described that I have very manic and impulsive patterns that follow with a long depression, even though they don’t mention bipolar disorder, they describe things that are in line with it and that I have recognised myself in hindsight. I am 18 and legally I can go to my gp (I’m from the UK) and take the necessary steps to get help or clarification. My sister did say that I should inform my mum that this is what I’m trying to do but I think I would wait till after I have an appointment.