multiple false positives

I have been a POS addict this week. I got a super faint positive on a first response on Monday so of course I had to take more to confirm lol. I ended up getting some of the walmart cheapies and they came back negative, I looked up reviews and figured it was too early since they aren't as sensitive. I went back to the store hoping to get more first response only to find that they were sold out so I got the cvs brand. More negatives, they aren't as sensitive. I finally got my hands on first response and Thursday afternoon took another test. There was another faint line! And it was even a little darker than the one I took Monday.  So I called my dr and they wanted me to get a blood test right away. It came back negative and was less than 0.6. I have never had a problem with first response tests before. Has anyone else had this happen??