Haha, I'm sure we've all just thought at some point or another "dammit, this would be so much easier if I was Japanese!". But we all have reasons for wanting to learn this language - I don't know yours, in the same way that you don't know mine, but the important thing is just to keep them in mind if you ever lose traction.
By the by - I wouldn't recommend doing long multi-hour shifts like the one you described. Little and often works best (for me, at least) - try to stick to between half an hour to an hour each day, and revise everything often. If it means having to re-read about something six or more times before you remember it, then don't worry - that's completely normal!
Now if it seems like you're just not getting anywhere even though you're doing everything right, the important thing is not to give up. Learning a language takes time, and the movement is like a glacier. If you take yesterday as a reference point and see how far you've come since then, you'll see little or no difference, but if you keep at it and compare today to last month, you'll see a big difference.
(This is why you'll never see someone rightfully claim "I learned -insert language here- in two months!"; it's just not possible. To get to a fluent standard in Japanese takes a matter of years, perhaps two or three.)
Finally, as ggenglish stated, practice what you've learned with the podcasts here if you're not already using them - they give you a much better insight into a real conversation than a textbook or webpage ever could
(Also, about using Japanese in everyday life - what I try and do is randomly and pointlessly try and think in Japanese when possible, when I feel like it. Like if it's raining hard outside, I might just think to myself, "hidoii ame desu ne..." Try it!
)
To summarise -
- Find a main learning method that works for you, perhaps one of the websites we listed, or maybe the podcasts and PDFs. Stick to it/them for half an hour to an hour each day, or an hour several times a week.
- If you're not using the podcasts and PDFs already, use them to get an insight into a real conversation!
That's all there is to it
ganbare!