I think I'm pregnant..

I'm 15 and I usually don't keep track of when I have sex and I have an irregular period but I had sex quite a few times before the 4th of July and a couple days after the 4th of July. And I'm starting to think I'm pregnant. I've been having all the symptoms. Swollen breasts. Constipation. Headaches. Fatigue. Bad mood swings. Frequent urination. Spotting. Nausea. I took a test and it said negative. I don't trust it. I know somethings not right with my body. I need help. Ion know what to do. Can someone give me advice please??