I Missed My Period 1 Times For 16 Days. I

I missed my period 1 times for 16 days. I took preg test 3 times but it negetive. Doctor suggest me tab deviry 10 ,once per day. Now i ask is there any risk to take the medicine. Is it effect on pregnency. My confusion is that if there is any mistake in preg test and i get pregnent then what is the effect of medicine. Already i start the medicin so what should i do.