Late period, faint positive, negative at doctors and nothing in ultrasound!!!

I've never missed a period before and after my first and only pregnancy. My child is now 8 months old who I exclusively breastfeed. However my period returned when my child was about 3 months old. I've had 5 periods since giving birth and they were all a 26 day cycle. My period is 12 days late and I'm experiencing pregnancy symptoms. I went to the doctor today to check abdominal tenderness and lack of period. The urine test came back negative there and they gave me a ultrasound. No infections found. In the ultrasound my lining wasn't thick enough for a period and it didn't look like a period was coming my doctor told me..... please help I'm so confused. If I am pregnant I'd be 5 weeks and 2 days . .. is it a chemical pregnancy? Or am I going crazy 😭