Hello, Anon. Thank you for posting.
It seems unlikely you are pregnant given your tests results are negative (and assuming you have been taking the pill consistently).
Side effects of the minipill might include:
Irregular menstrual bleeding.
Decreased sex drive.
Small ovarian cysts can develop in some women.
Side effects typically happen within 3 months as your body adjusts to the pills, but this can be different for every woman. Call your GYN or speak to the office nurse and ask their opinion on this to ease your mind.