Melt and pour already has everything in it to make it lather.
How does a small slice of plain base (before melting or adding anything) lather? If that's ok, then it's something you're adding which is reducing the amount of lather. If you can't figure out what, post a detailed account of how you're making soap and I'm sure someone will be able to find the culprit.
If the base doesn't lather enough on its own, then all you can do is buy a better type next time.