What's wrong && why haven't I started

My last menstrul was August 23 && I had unprotected sex on September 5th , I keep taking pregnancy test and they are still saying negative I even took a blood test and it was negative.. So not to long ago I had a really bad pain in my right side , it was unbearable and it hurt really bad when I moved or breathed. So I went to the hospital the next morning and they did a transvaginal ultrasound and told me something was swolling were I with haven't had my perod or I'm about to start , well it's been over a week since they told me that and I'm still not on my perod ... Is there any reason I'm not on my period & what can be wrong with me ?