I have taken about 10 preg. tests. I had 2 come back as positive yesterday and then when I took another this?

morning to confirm it, I got a negative result. I had the positive results show up on a generic brand from Target store. I got the negative results today on the First Response Early Detection test. All of the other tests have been negative. I am over a week late on my period and Im confused and nervous. Should I take another test? Could it be that I am pregnant? What do you think? I posted about this last night but after taking the tests this Am I am not so reured anymore Thanks for any advice.