testing positive and negative?

Hey guys! I took a first response pregnancy test this morning, and it's obviously positive. I also took one of the Walmart off-brands, which was also very faintly positive.. I just had a MC 08/04, so I let my excitement get the best of me, and I went it and bought a clearblue with the plus signs.. from what I can tell, it was negative or only a vvfl.. has this happened to anyone else where one minute you can get a positive but later a negative? I feel like something may be wrong..😕