Hi.. My Double Markers Test Is Positive... I'm 33 Years

Hi..
My double markers test is positive...
I'm 33 years old and this is my 3rd pregnancies..
I and my hubby hv no history of syndrome down baby..
While they took my blood i'm having severe diarrhoea and vomiting..
That time i'm already 17 weeks pregnancy..
Did my condition can cause beta hcg raised and its that possible the result is not accurate??
Tq so much for the guidence...