There may be several reasons, many have to do with your mental attitude towards the code of communication you are trying to learn. Some suggestions:
1. You may think in English what you want to say, and then try to make it fit into Spanish. This doesn't work; don't try to start from zero: Read first as much as possible, so you get used to the patterns of Spanish and learn words and what they mean by using the dictionary. Then write sentences in Spanish. Next, speak them in Spanish. Finally, listen carefully and try to make sense from the spoken answers you get back from the persons with whom you are speaking
2. Word order is often different. We say in English, for example, The White House. The [article] White [adjective/ noun modifier] House [noun].
In Spanish, you have to say La [article] Casa [noun] Blanca [adjective].
3. We don´t assign a gender to things, but Spanish, French, Italian, German, etc. do. We say the knife, the fork, the spoon. In Spanish you say ¨"el cuchillo" [masculine], "el tenedor" [masculine], "la cuchara" [feminine]. Your dictionary tells you if a word is a masculine noun (n.m, for nombre masculino. or n.f. for nombre femenino).
4. We use verbs in English in a different way than in Spanish. To indicate the person, we use the different pronouns but the verb remains practically unchanged: I read, You read, We read, and so on.
In Spanish, you have a different verb form corresponding to each pronoun: Yo leo, Tú lees, Nosotros leemos....
5. All infinitive verbs in Spanish end in -ar, -er or -ir. Estudiar, comer, vivir.
6. Each one of these three groups has definite endings for each verb tense. For example, in the Present tense:
-ar: o, as, a, amos, ian/iais, ian. Estudiar: Yo estudio, tú estudias, él/ella estudia, nosotros estudiamos, ustedes estudian --or vosotros estudiáis--, ellos/ellas estudian.
Yo leo, Tu lees, Él lee, Nosotros leemos, etc.
3. Get your ear in tune with the foreign language you want to learn. First listen to the news, preferably international news, in English (CNN is a good source). Memorize the substance. Then listen right away to the news in Spanish, and you will be surprised of how much you grasp and understand (RTVE.es is a good source with its Telediarios and Noticias 24 horas, available in internet).
Always adopt the attitude that you do want to communicate something to somebody else.Good luck with your efforts!