is it possible you can ovulate twice?

So I took a opk test on the 14 which was positive had sex on that day and then again today which is the 21 and it's dark again so I read online how some women ovulated before finding out they were pregnant by using a opk before taking a hpt I know I'm not pregnant but my partner thinks I am but it's too early to even tell but why would I get a positive opk twice?