Why am I not good at Spanish?

First of all you need to know that learning a language is not easy, so do not worry if sometimes you are struggling with it. It is important to practice as much as you can, to do the homework in the target language and be curious about learning new words.Secondly, you need to be positive. Sometimes things might not make sense in your head, but with patience and practice you will start understanding more and things will become easier. If you like reading, try to read a book in the target language or watch a movie with subtitles. Of course, if you have the opportunity, travel to the places where the language is spoken. You will fall in love with it and you will be more motivated to learn it.