13 days late

Hi everyone, so I am 13 days late. I do have irregular periods so I do not want to test because I do not want to see a negative test. I do plan on testing Tuesday if Aunt flow still hasn't showed up. Anyways, there are a couple things that have me a bit confused. First, my lower back has been hurting for 2 weeks which is not normal for me. Second, my husband and I had sex the other night and about 5 minutes after I had horrible cramps (no bleeding). They were so bad that I felt like I was going to throw up, which has never happened before. I just need some advice to clam my nerves. thanks.