The probabilities: you have been diagnosed with it and you tend to doubt it and maybe denied it but you rediscover you have it, you strongly believe it, while doing so. The probability of that happening by chance is low. Especially when you have denied it (a few times). It would be more likely if the diagnosis were based on your denial and belief, but still the change in perception of yourself is specific enough: likely BP.

If you were strongly advised to go to a psychiatrist or needed hospitalisation, the chances of a mistake are even lower.

The longer you have been observed, the smaller that change.

It's very good to actively doubt it, question it, see how you might fool yourself, because it will make it more likely you have it when you believe it.

But don't do it obsessively. It's not worth it (but it is worth another diagnosis ).