Cramping and levels are high

I’ve been having really bad cramping so I finally called my doctor today. They thought I was 5 weeks 1 day as of this morning. They had me do a blood test today and my levels came back at 18,000. So now they are thinking I’m more like 6 weeks. How can this be when I’ve been tracking ovulation daily with test strips prior to becoming pregnant? My ovulation came back positive 1/16 My last period started 1/4 and was seemingly normal. The cramps have been extremely intense in the center and no bleeding at all since January 6th. I was not feeling well and took a test on 1/20 which was negative but got my bfp on 1/30.