No Orgasm in a month

So I've been with my boyfriend for 3 years and we have been sexually active for 2. Most times, I cum fairly easily with a combination of vaginal and clitoral stimulation. However, for the past month I have not had an orgasm from any of our encounters. Don't get me wrong, I really enjoy the sex, I'm just confused on why I haven't been able to finish since it hasn't happened before.