Hi, I Had My Periods On 18th Feb,2016 And I

Hi, I had my periods on 18th feb,2016 and I did the home pregnancy tests on 30th march and 3rd April..Both were negative. I saw my doctor on 4th April and she did a Urine pregnancy test which was negative too. She asked me to have regestrone 5mg twice a day for 5 days and ethinylestradiol tablets 0.05 once a day for 5 days.
I started the medicine on 11th April and finished it on 15th April. But I got no periods. So I took a hpt again on 24th April and it came out positive. I am happy but I wish to know can it be a false negative.. And will the medication that I took have an adverse effect on my baby... Plz help