It's important to note that the sentence structure is slightly different in Spanish than in English. In Spanish, you use "yo" (I) and "siento" (feel) before "solo" (alone).
Here are some other ways to say "I feel alone" in Spanish:
* Me siento solo/a. (More common and informal)
* Estoy solo/a. (More formal and emphasizes being alone)
* Me siento muy solo/a. (Emphasizes the intensity of feeling alone)