It seems to me that you lack both the aptitude and the motivation to achieve your goal, as evidenced by your lack of progress.

Frankly, someone with a goal such as yours should be able to attain a level of "a bit higher than N4" within a year through osmosis alone.

Back in early 1999, an erstwhile colleague of mine (let's call him Matt, for 'twas his name) at NOVA had ambitions of studying at Osaka University and was starting to study Japanese, basically from scratch. As well as working at NOVA during the week in the evening, he moonlighted at a restaurant on weekends, with the primary purpose of improving his Japanese. He spend about 35 hours a week, and much of his income studying at home, sometimes with a private tutor.

I, on the other hand, was an old-school otaku (predating weebs), and my self-taught, self-assessed level prior to arriving in Japan in late 1998 was, maybe, N3.5, so I had a head start on Matt.

Anyway, we resolved to both take 一級 (the old N1) at the end of 1999 (why bother with the lower levels). He studied diligently; I continued to read Young Jump. We both just missed out on passing first time. Matt scored slightly higher than me.

We both took the test again in 2000, and both just passed. Again, Matt scored slightly higher.

Matt also passed センター試験 and got into university as planned, through sheer hard work.

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tl;dr: see opening sentence.