Sorry! I'm not good at explaining.
I am sorry that my explanation is difficult to understand.
I'm sorry, my explanation wasn't enough.
I am sorry for not explaining well enough.
I'm terribly sorry that the explanation of mine was difficult to understand.
I am sorry for not explaining sufficiently.
I am sorry for saying ambiguous things.
I am sorry to have said something so harsh.
I apologize my explanation is insufficient.
Sorry, I can't understand you.
I am sincerely sorry for the insufficient explanation.
I am sorry for my hard to understand explanation.
My explanation about that was lacking.
I am terribly sorry that my explanation was not enough.
I am sorry that I couldn't convey that well.
Please forgive me for my poor [lame, unsatisfactory] explanations.
I am sorry for the lack of explanation.
I am sorry for not being able to readily understand that.