What Causes Missed Period And Tender Breasts?

I am 31, have been diagnosed with premature ovarian failure and have been taking Cyclo Progynova for 2 years. I have always had a menstrual period during the week between pill packs. However, i recently missed my period. My Doctor said not to worry and continue taking the pills normally. Additionally, I am experiencing breast tenderness and enlargement. Could I be pregnant or is it possible my hormone levels are off?