If you’re using proper hg branches, then you should be able to use the –only-branch option:
hg log --only-branch my_branch
That will show the changesets only for a given branch.
Edit: Looks like “–only-branch” is deprecated, but depending on the version of mercurial you use it will still be there. See https://www.mercurial-scm.org/repo/hg/help/log . If your mercurial is too new, you may only have the “-b”https://stackoverflow.com/”–branch” option.