I Haven't Had A Period Since December 27,2015. I Had

I haven't had a period since December 27,2015. I had needle drops of brown blood on January 26th. Negative blood test on January 28th. I have a normal 29 day cycle. I had an ultrasound on January 31st and the tech said the endometriom is thicking. So my question is could I still be pregnant? What does it mean the endometriom is thicking