What Causes Feeling Of Vomiting?

Yesterday in the early morning around 3:30am or 4am I was woken up feeling like i had to puke and my mouth began to water a lot. I actually did not puke. This happened from 4am to about 6:30am like 3 times. My husband and I have been trying to get pregnant. I took a 1st response test today but it was negative. Could it be too early to detect?