false positive?

I currently have a cold and started taking airborne yesterday to start getting some extra vitamins in my system. AF is due on jan 1st but I decided to take a test yesterday just incase so I am not taking medication that I shouldn't be taking if I am pregnant. I took a test yesterday waited a couple minutes and threw it away assuming I tested to early. When I was taking out the bathroom trash today I noticed a faint positive on yesterday's test..... I decided to take another test today and got a more clear positive. After beginning to question everything I went to the store and got 2 other brands of test, including a digital. Both came back positive.... could these be false?