I know you’ve gotten a lot of encouraging and well articulated responses, but I wanted to add my thoughts as someone who has only been studying for around three weeks. I’ve been struggling with a lot of similar thoughts, so I thought my perspective might be helpful. (Spoiler, it’s really similar to a lot of stuff people have said already)
One thing that has been reassuring for me is to think about how long it took me to get to the level of mastery I have with the English language, my native language. It took forever!! I’ve been learning so many new things, like grammar and vocabulary, for my whole life. I’m 24 and I’m still taking English classes in college that are teaching me new ways to use English effectively, and there are still things I get wrong all the time.
That’s not to say that learning Japanese to a level where you can effectively use it will take you 24 years. However, it is to say that even once you’ve gotten to a level you’re comfortable with, learning a language never really stops. When I think about that, it’s easier to tell myself this:
The time will pass anyway, regardless of whether I’m learning the language or not. Even if I don’t learn as quickly as I hope to, or it’s really difficult and I want to quit, I will eventually learn the language to whatever level I desire as long as I just do not stop.
That being said, I agree that sometimes it really does feel like you have to know a lot of vocabulary to get anywhere with the language. I’ve found that even when it does feel that way, I slowly learn some words here and there even if I’m not specifically trying to learn them. I think this is what makes immersion and repeated exposure to words in context very powerful for me. If I keep reading and hearing words over and over in similar, simple sentences, I slowly learn them even if I have to look them up several times. I may not understand a sentence at first because I don’t know some of the words, but the more times I see those words, the more opportunities I have to learn them.
I’m not saying you should go out and try to read books right away, or watch your favorite anime without subtitles. But try to find ways to expose yourself to simple sentences over and over. I’ve found that a textbook has been a great resource for that. I’m working through Tobira 1, but there are lots of other options that may fit your particular learning style better. There are Anki decks that teach you words in the context of sentences in a spaced repetition system, similar to how WaniKani works. Repeated exposure has helped me a lot.
All that to say, you don’t have to beat yourself up for not being able to read a sentence because you don’t know the words. Try to remind yourself that even when you can’t comprehend a sentence, you’re actually still learning. It’s okay to have to look things up. It’s expected, even! Don’t you have to look up stuff in your native language sometimes? Aren’t there words you have to learn to fully understand a sentence, even though you’ve already mastered your native language? All of the very same things you’re doing now, the same things you’re struggling with in Japanese, are things you did and struggled with when you were a kid learning your native language!
I definitely don’t know the best way to learn a language, and there are a bunch of immensely more knowledgeable people here than me. Nonetheless, these are (some of) the things that have helped me so far, so I thought it might be useful to hear from me as someone who has similar thoughts to the ones you expressed all the time. I have to remind myself of these things often, basically daily, but it’s slowly getting easier and easier to learn the language without having to remind myself!
Please keep going if you really want to!! You’re not alone with these feelings!!