why is my welding inconsistent?

You did not mention what welder you are using.
Flux core or gas and solid core?

What are your settings?

Sounds like your temp is too hot if it's burning through Which means you should be concerned about your settings.
Turn the heat down a click and try a sample piece until,you get it where you want it.

Do you have an auto darkening mask?.....gosh I love those things.