How common is it to get repeated false negatives??

I have been nauseous for over 3 weeks Had cramping and spotting for 2 1/2 days. On the 13th-15th of February. Since then i have remained nauseous, had bloating that seems very tight and wont go down, headaches, lower backpain, heartburn, super thirsty and have to pee about once and hour. Also constantly tired. I am so sure im pregnant, but it has been two weeks since spotting and im still testing negative. Could i still be pregnant?