Why am I not 😔😔???

OK so according to Glow I'm late on my period it's been 4 days late now and me and my s/o had sex a day before my period cycle even started and he came inside me. I took a pregnancy test last night a Early First Response and I just don't understand Why it came out negative. Now today is my 5 day in my cycle. Can any of you ladies please help me understand or should I just go to the doctor and ask for a pregnancy test there??