I have been with my fiancé 4 years and we have not been using protection for 3 years I am worried I can't get pregnant what should I think? Each month my period comes a week sooner than the last, they are getting closer and closer together. What could be the reason?

Since you have been trying for three years, it is time to visit your doctor. They will likely do some initial testing on both of you as there are a number of possibilities as to why it hasn't happened already. Age is sometimes a factor as well.