Is it permissible to interpret a single dream more than once, especially if the dreamer is not convinced by the first interpreter's explanation? And is asking an interpreter about the interpretation of a bad dream considered among the forbidden acts of speaking about it?

There is no harm in interpreting a dream more than once, for a vision is not meant for the first interpreter at all, but rather for one who correctly grasps its meaning. This is evidenced by the Prophet’s (peace and blessings be upon him) statement to Abu Bakr (may Allah be pleased with him) after he interpreted the dream of the shade: “You got some of it right and some of it wrong.” As for speaking about a vision, it is recommended not to speak about it except to one whom you love. If one sees what he dislikes, he should not speak about it to anyone, because it might be interpreted in a disliked way and then come to pass. It is permissible to ask a scholar of interpretation about a vision.