Please help!

I'm a bit confused, I was testing for ovulation since Wednesday oct 15. I got negatives on 15 & 16 which are Wednesday and Thursday. Forgot to test on Friday and when I decided to test on Saturday oct 18, the two lines were so close in color that in my opinion it was a positive. On Sunday the 19 it also looked very closed in color but not as the one on Saturday the 18. Does that means I ovulated on Sarurday the 18th or Sunday the 19th? Could it be that I could have tested pos on Friday but forgot to test and ovulated Saturday? I'm so confused on how to go about opk's. I was feeling so much pain on Saturday the 18th only that I assumed it was Ovulation pains :/