Positive Pregnancy Test ALL THE TIME!

I know it sounds silly, but I can go to the store right now and buy a test and use it and it would be positive. Actually I just did to show someone. This has happened to me well over 100 times (I keep buying them in disbelief Even though I know it's a waste of money, they are never negative.) Maybe one time I hope it's going to pop up BABY. :) I've been turned down for MRI's because my blood work has said that I'm pregnant, which I'm not, I never have been. I've been to 3 doctors so far. One was baffled, one said I was fine and one idiot doctor said I was having a miscarriage every single month. Which is not the case. I've tested it.. . I plan on having children soon and wandering if this is going to mess with me. If somebody out there has heard of anything like this please please help. I have done so much Reaserch and come up with little. It really sucks if I'm a few days late I can't just go buy a pregnancy test.. Turns out it's always stress but I would still like an idea as to why this is happening.