Is it possible to be pregnant and for test to come back negative??

I had unprotected sex, he used the pullout method I got my “period” 2 days early, but it was a weird “period” I usually have long heavy, painful periods that last 8 days, the shortest my period has EVER been was 6 days. This period only lasted 4 days and I had absolutely no cramping I have really really bad cramps I even have to take medicine for my cycles I didn’t have to take anything. My period stopped After 4 days & 3 days later I start spotting light pink & having mild back cramps and little sharp abdomen cramps. When I eat I suddenly lose my appetite, or become nauseous during the day. My friends said maybe I’m still on my period, I’ve took 3 pregnancy test and they all came back negative, but I’ve heard that sometimes people can be pregnant and still have negative test. It’s been 4 weeks since it happened & so it might still be early ? It’s just weird because all my life I’ve had really painful periods & suddenly after I have unprotected sex I have periods that only last 4 days? I’m asking for a second opinion?