What Causes Nausea And Headache With Negative HPT?

hey, can you help me, im 21 and the last week and a half i have experienced headaches, sickness but not been sick, all day everyday, bloating, change in nipple area, loss of apitite. I have done 2 pregnancy tests and both say negative. If i am pregnant i am only 1-2weeks. Please help! what else could it be as the tests say negative?