I recently read of books called ‘Q’ and the Gospel of Thomas. Interesting
reading! I was wondering what you thought of them and their authenticity.
Why are they not included in the Bible?

Actually, much of “Q”-the hypothetical source of material common to
Matthew and Luke-is in the New Testament. Let me recommend you read an
introduction to the New Testament (e.g. Merrill Tenney’s New Testament
Survey), and you will be able to answer the first part of your question.
As for the Gospel of Thomas, this is a gnostic work dating from after the
time of the N.T. That is one reason it is not “included.” And, as you will
have realized from reading it, there are a number of contradictions with
the N.T. (For example, Thomas teaches that women are not worthy of eternal
life, and that esoteric knowledge is how we become spiritual.) This
spurious “Gospel of Thomas” has no connection with the true apostle
Thomas, who faithfully followed the teachings of his Master, establishing
the church in India and dying there for the faith.

Douglas Jacoby