Having both BPD and AvPD seems very unlikely to me as the behaviour in the two is almost completely opposite, even though low self esteem is a major issue for both.
I sometimes feel like I have the emotions of BPD with the behaviour of AvPD. I have borderline traits but the AvPD is so much stronger.

We can give our opinion on what we think but no one here can give you a correct diagnosis. But for what it's worth, I also don't think your posts sound like someone who has AvPD.