Hi Linda!

So sorry to hear that you failed the N4. This could be a cliche but don't get discouraged by that.

I know studying alone is so hard for you, if I were you I would try finding a study buddy or booking a lesson with Japanese teachers here on Italki or elsewhere. Looks like you need someone to tap on your back.

Regarding a good idea to improve your Japanese - it's a very generic question. Could you be more specific? When you failed the JLPT, Where did you think you goofed up? When you try to study Japanese on your own, what in Japanese made you feel difficult to carry on the self-study (e.g Kanjis, pronunciations,specific grammars..)?