chances of pregnancy?

Iv had periods, taken pegnancy tests that were all negative and had an ultrasound done a few weeks ago to look for a cause of my pelvic pain (would have been 6-7) and a pelvic MRI (I would have been 13-14 weeks) 
They didn't say I was pregnant but I didn't ask. If I was pregnant would have they seen something on a pelvic ultrasound (I would have been 6-7 weeks at the time) or the MRI (14 weeks if I was to be pregnant? 
The doctors have done 2 urine pregnancy tests and they were both negative! 
What are the chances that I could still be pregnant and it has gone unnoticed?