I need some reassurance...

Just started my period today. I really thought it wouldn't come. Even though I turned 40 last week, I have 2 amazing kids, 11 and 8, and I am in very good health. I have never smoked. I am a runner. I eat right (mostly). My last antral follicle count was perfect. Doctor says I have the ovaries of a 25 year old. I used ART to have my 1st child, but didn't need it for my second. My husband and I have always felt like our family was missing someone- like it wasn't quite complete. I was 8 dpo a few days ago when I got a positive HPT. Today, I started cramping and bleeding heavily. Today's HPT was negative. My doctor suggests taking another test after I stop bleeding and then come in for an exam on 2/10.