I Had My Period On 17 Th December Then I

I had my period on 17 th December then I had sex on 29th December it waz a unsafe one means no precautions were taken... On the month of January my periods did not appear which waz unnatural as I get my periods on time I was afraid of pregnancy & had a test at home using prega news twice but both results were negative & I haven't got my periods yet..wat must i do now. I don't want to get pregnant now