In the last 4 months i've began having spotting the day before my period, what could cause this? my cervical exam was normal.

Maybe nothing wrong: I don't see anything terribly wrong in the symptom you are describing. Although, periods are expected to be heaviest on the first 2 days, sometimes, in some women it may be normal to have a little different routine. If that's the only symptom and, like you said, your cervical exam is normal, i might just watch it for now.

Hormone production: Spotting a day before your menses on a regular menses may be considered normal and just marks the beginning of your peroid. However, it may reflect less hormone production during your cycle. There can be anatomic reasons as well that only an ultrasound will pick up such as a fibroid or a polyp inside the urerine cavity.