Not sure why I am getting negatives?

Hey all this is our first month trying, I used a the clear blue opk to find out when I was ovulating and we had sex that whole week. I have had some symptoms but got a couple negative tests, I woke up with cramps yesterday thinking I was going to start my period the next day (today) but I woke up with nothing, no spitting at all, even though I normally spot every month a couple days before. I took a test this morning and it was still negative but I have mild cramps and my lower back is killing me! I am using the Dollar store ones bc I was told they work just as well, am I testing to early or do you think it's the test I am using?

Any help would be great!!! Thank you!!!