Putting on my serious face

Today I got serious about learning English.
In the Dutch high schools it is normal to study English, and I was honestly quite bad at it. It wasn't until I went to an English speaking country once that I started to understand it a little bit. +At+ that time I was happy with producing something which +that+ was just slightly understandable.
Now I have started learning Japanese, using English, I have to conclude that both my vocabulary as +and+ my grammar sometimes don't add up. Stuff I don't understand keeps showing up and when +I'm+ studying Japanese +even though+ English isn't my main focus, thus I tend to think it might hurt my study process.
Now I am wondering about what I can do to improve my English, since the most resources are either a little difficult to understand or way too easy. Also I feel like my sentences don't seem anything like those of a native. How can I become like a native speaker?
Also, since I will be a student starting +in+ September, I can't afford to hire a tutor nor do I have a lot of time to study.

I don't really know the Italki community very well, but I hope I can get along with all of you.
Thank you for reading!

Your English is actually really good! If you look at my corrections there weren't that many! Unfortunately I don't know any English learning websites, but I think you should take a couple of hours and just write a notebook entry everyday or every other day. Also try to find someone to practice with. Good luck!