I have a cyst on my left ovary that is causing pain, pregnancy like symptoms and very heavy menstration. I went to my OBGYN on 4/10/2012. A blood test for pregnancy was negative so I went back three days later for an ultrasound which showed the cyst has grown 2 cm (to 6cm) in a little less than a month. The ultrasound also showed a fluid sac in my uterus. To me it looked like a gestational sac ( I have four children and have had many ultrasounds). My OBGYN said she isn't worried about it but couldn't rule out that it was a pregnancy. I ovulated sometime between 3/26 and 3/29 and we had sex during that time without protection. My period came four days early and was light compared to usual. It also only lasted 72 hours and I spotted for another 12. It usually lasts five full days. I am also having symptoms of headache and slight breast leakage. I had my fourth child nine months ago but was unable to breastfeed and my milk dried up completely. My question is could the egg have implanted late enough for the blood test to be negative and still show up on an ultrasound three days later? I took a hpt this morning (4/15) and it was negative. If its not a gestational sac what could it be? My period ended the day of the ultrasound, could it have been blood?