What Causes Yeast Infection During Periods While On Sprintec?

I am 19 years old and im 5 2 weighing 157 and I ve been on Sprintec for almost a year now. Every since I got on the pill, i get a monthly yeast infection. Either right before my period or on my period. I haven t wore tampons in over 5 months because of the pain. I scheduled an appt with my doctor and the swobbed me and said so herself it was indeed a yeast infection. She then told me to treat it like i always do and wait for the results to come in. A month later, i never got a call and i came back in because i had another yeast infection. The doctor begins to tell me she doesnt know whats causing it and doesnt even know if it is a yeast infection. Ive asked her many times if its my pills and if she could change my pills to see if thats the problem. She told me shes 100% sure its not my pills, then tells me to change my toilet paper, soap, and use all natural pads. My Question is, if its not a yeast infection, then why do over the counter medicine treat it? Every month i use monistat and it goes away 3 days later. So i took it upon myself to try another doctor to get a second opinion. Could my pills be causing this?