Last intercourse I had was on July 29th 2016 and I took an emergency contraceptive the consecutive day. My period was then delayed by a week and came on 5th August, though it lasted for 2 days and was not too heavy and I interpreted it as implantation bleeding.
Since then I have had periods on 31st August for 3 days and 28th September for 5 days. (But people do at times get periods with pregnancy)
I did get a vaginal ultrasound done on 12th October and it showed no gestation sac. The doctor said that there is no pregnancy as of yet.
Is it possible that the gestation sac has not yet developed and I need to get another ultrasound a few weeks later. Can I still be pregnant ?

Home pregnancy test - negative
Minor PCOS
hypothyroid - recent report shows increased t3 and t4 but normal TSH.