According to expected due date, you ovulated around 7th January. You did unprotected sex on 4th January which is unsafe or fertile period. So chance of being pregnant is there.
First of all, you do a blood test
scan to confirm intrauterine pregnancy
with gestational age
. If you get both negative test, then you need not to be worried. It may be due to stress/ hormonal imbalance.
In case of positive test, you have to undergo medical abortion
under supervision of your doctor to avoid unexpected vaginal bleeding. So consult with your doctor regarding this.
Practice safe sex by using safe period/OCP/ Condom etc to avoid unwanted pregnancy & unnecessary vaginal bleeding. Be well.