Hi, I Have Been Menopausal Since 2010. I Take Prempro.625/.5

Hi, I have been menopausal since 2010. I take Prempro.625/.5 mg daily. However, recently I ran out of my pills and therefore went without for 5 days. I then started again, then stopped again because I had surgery and the hospital I was at did not carry Prempro. I went without for 3 days this time. I started again and have been on for 3 days. But, just now when using the bathroom I realized I was bleeding. Am I correct in believing that this is because of stopping and starting the Prempro? Are there any concerns that I am not aware of?