My voice always feels very strained, tense, and tired. What can I do to fix this?

See your doctor. You probably need to see an ear, nose, & throat doctor to have them look at your vocal cords. You could have nodules or polyps on your vocal cords. The ENT can let you know if there is anything that needs to be done after they examine your vocal cords.
Voice strain. Voice alterations can be from overuse (are you a singer or public speaker?), or from growths on the voice box, or from improper coordination of the laryngeal cords (helped by botox) and sometimes by psychogenic causes. See your otolaryngologist to sort this out.