The efficacy of the birth control takes atleast 7 days to get established. You should use additional contraception like a condom for atleast 1 week-10 days since your wife has switched over the birth control only 4 days back.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.