When you're hot, you're hot, and when you're not, you're not. Sometimes there seems to be no rhyme or reason as to what causes your sexual response (or lack thereof). Many factors determine how turned on you are at any given time — the quality of communication between partners, self-esteem, stress, feelings of warmth or closeness, family problems, stimulation or lack of stimulation, fatigue, aerobic fitness, and religious beliefs all affect your libido.