I don’t know if I should be worried if I’m pregnant

Patient: Hello, I’m about 3 weeks late for my period and have absolutely no signs of it. Usually without birth control my periods last about 7 days and are very heavy and painful including back pains and horrid cramps before and during it. My last period was March 5th and only lasted two days with not a lot of heavy bleeding. The last time I had sex was around Feb 13-22. I’ve been experiencing more than normal fatigue, headaches, and nausea and am very worried about being pregnant. However I took four at home tests that came back negative. The last one I took had a faint positive line for a minute but then it went away. Should I be worried? or do you think I really am not pregnant?

Symptoms: Fatigue, late period, headache, nausea