Do you think I could be pregnant?

I have a brown line on stomach below my belly on going down. I had unprotected last month but got my period this month. I've never had a brown line before on my stomach and like a few days before i started my period i got it and it still hasn't gone away. Some days i look bloated. Sometimes i have no energy/fatigue. I get really emotional or irritated sometimes and my are sore. I've also been having light cramps or twinges and I've been getting really nauses. I took a pregnancy test like 1 day before my period started and also like yesterday and it was negative. My sister said the only way to get a brown line on stomach means your pregnant but i tried to tell her I'm not cause i started my period this month on like the 16. She thinks I need to go to a doctor to have a blood test done. My period is usually irregular. My period ended about 2 weeks ago. What could the brown line mean and why is it still there and why am I still having symptoms even though I got a negative pee test? Should i go to the doctor?