3 positive opks in a row.

Stacie • 31 and carrying an Autumn baby
I've just had my third positive opk in a row. The first had lines the same colour, the most recent two, the test line was darker. 
​Anyone know what that means, and if that's normal? I thought you had one surge and ovulated in the next 24 hours? 
​I do my tests at 8pm each night if that makes any difference and have been testing for five days altogether. 
​Thanks.