How long have you been learning, and how much do you practise? If you've been learning for three years and still don't know hiragana properly then I'd say give up, but otherwise it may be just a normal part of the learning process. As new stuff piles up on top, the older stuff that you feel you ought to know can get displaced. I periodically go through stages where I feel I'm forgetting stuff I used to know, like misreading simple kanji that I learned a year ago. If it's any consolation, as you read more and more Japanese, it becomes easier to recognise whole multi-character combinations without having to step through consciously recognising each character individually. This is similar to English, where fluent readers pick off whole words at once without spelling them out letter by letter.