Am I pregnant or not?

I was supposed to start my period last Tuesday. I had surgery last Wednesday for a cyst on my tail bone. They gave me pregnancy test before I went under for the operation & it was negative. I took a test a few days later and still negative. It has now been 9 days and still no period. I was on birth control for 13 years & periods were always spot on. I decided to get off of it November 2017. December's period was right on time and normal. I don't know if it's because my body & mind has been under alot of stress or what. I called my OBGYN and they told me to keep taking tests every few days. If I still don't start and tests are negative by next Monday then they will run some tests on me. I haven't even had any symptoms of menstruation like cramps, moodiness or bloating. Although my nipples have been extremely sore the past few days. What do you all think? Am I over thinking this, stressed out and that why I haven't started or could I really be pregnant and keep getting negative results?