Hi, and thanks for your medical question on eHealth forum!
One reason the test is negative is that you tested early. Since you had periods on 19th April, you should wait until 19th May before testing. So you can test now again and see. If the result is negative then two main things will have to be ruled out, hypothyroidism and PCOS.
Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your gynecologist once. Hope this helps. Take care!