how do i tell when i ovulate​?

Courtney

I was spotting on 17,18,19 took my miriana out Wednesday the 20th then I spotted from the 20th till the 22nd. But between all those days I only had to wear a panty liners or not at all it was so light. some times it looked so light it was orange. My doctor said I should ovulate this weekend but I keep taking ovulation test and they all come back negative. help!!!!