Pregnant before AF after natural miscarriage

Amber • 28 yrs old-married for 8 years. Lovebug born 11/3/09 BFP after miscarriage and before AF. Due end of August
Is this normal? I miscarried 11/9 and quit spotting by 11/13 and my levels were 157 at that time. On 11/18 I had a negative test. Today is two positives when I tested because AF never showed. How do I calculate a due date? Is this even real?