As no natives are answering for the moment, I'll give you my proposal: "I lack (of) self-control".

用地道的美国语法，“I don’t have any self control."

In addition you could say: I don't have self-discipline.

你应该说： "How do you translate xxxx?

Usually a person with no self-control will be considered "impulsive" (but not always). http://www.merriam-webster.com/dictionary/impulse?show=0&t=1360210585 b : a propensity or natural tendency usually other than rational