It's a phrase that expresses doing something repeatedly, often something you know you shouldn't be doing or have already done. It can imply a sense of frustration, regret, or even amusement depending on the context.
For example:
* "Lo estoy haciendo de nuevo, no puedo evitarlo" (I'm doing it again, I can't help it)
* "Lo siento, lo estoy haciendo de nuevo" (I'm sorry, I'm doing it again)
* "¡Ay, no! Lo estoy haciendo de nuevo" (Oh no! I'm doing it again)