Hi Lindsey -
I'm a doula, so I know quite a bit about the female reproductive system. I would say this is anxiety playing a MAJOR role here. Even if you feel you've been more stressed out before and your period still came on time, stress can build up in your body - to where your new state of "normal" - is really an anxious state. Your body has become so used to the stress hormones throughout your body, that it send them out anyway, because that is what you've trained it to do, subconsciously. I am in this position as well.
You say your husband had a vasectomy - I assume you two have children? If you've ever had children, this dramatically decreases your risk of ovarian and uterine cancer. Have you breastfed? This also decreases your risk. 27 years old? No family history? Ever been diagnosed with breast cancer? - I'm assuming "no" on that last one - I would say your chance of getting some type of reproductive cancer right now is next to nothing. zero. zip. nada.
Maybe due to stress you ovulated late? This will delay your period. Any recent cold or viral infection? This may delay it as well. Give it another week or two. If you're still concerned, go to your GYN just for peace of mind. But I HIGHLY doubt there's anything sinister going on.