Hi! Just wanted to chime in that I felt that way about the cases too, though my problem was when someone tried to generally explain cases to me when I just started learning - I didn't really know English grammar, or grammar in general, as a native speaker so had to learn that first to understand Russian. It seems you already have a grasp on that. I think the trick for you, however annoying it is(and it really is because for a long while you really can't say anything or read anything), is to just go through the cases one at a time and master them before you move on. Get a good textbook or workbook that has tons of exercises where you are just constantly putting words into the correct case, finding which verbs require the case, memorizing specific grammar constructions that require a particular case(eg. dative - МНЕ холодно, ЕМУ 6 лет ect), and just writing out random series of adjetives and nouns and put them into every case as practice(we had to do this in my first year a lot).

I promise that when you do this the cases just get ingrained into the way you think, you will remember specific phrases as well and you will no longer have to "translate" in your head like "'I am going to walk the dog in the park'...so 'the dog' is in accusative.....'I' am in nominative...'in the park' is prepositional...okay."