Missed period

Tammy

My period was expected October 3 took pregnancy test 3 days after all negative went to hospital for pain on October 10th they did a urine blood and ultrasound all negative for pregnancy took another test on the 15 still negative went to my obgyn today and positive pregnancy test and they did an ultrasound showing a sac that measured 4 weeks waiting on my blood work .could I have ovulated later so confused