pregnancy and Mirena ?

The last time I had sex was July 24th and we didn't use a condom but he didn't pull out because he didn't have to, I helped him with that , if that makes sense 👅 haha but anyways.. I have the Mirena for my Birth Control so I thought I was good. So my period is always very regular it comes every month on time! I do have two kids hence why I has the Mirena.. So I got my period right after we had maybe one to two  days after we had sex. So it's the 28th of Aug and I still have not gotten my period. I took two tests and they both said negative I'm maybe thinking it's too early... ?? I am getting like really dark like brown almost black.. I have had some cramps and a sharp lower pain in the stomach by my hips bone... Anyone know what's going on or had anything similar? I am going to wait about a week to see my doctor..