positive test after stopping birth control

💜sherry💜Due:4/7/18 with my 2nd💜

Asking for my sister. She stopped her birth control on June 20th. She had some spotting on the 21st and 22nd. She never got her period though. She took a test 2 weeks ago and was negative. She took a digital today and it was positive! So my question is when did she ovulate if she never had a period? I'm 5 weeks 4 days pregnant and we're trying to find out how close we are but no dates to go off of. Thanks!