Okay first I'm 20 years old in good health me and my boyfriend have been trying to conceive for a year
My last period was 7/12/13 that's( July 12 -2013 )
We had sex on the days we are suppose to prior to ovulation and my fertile window I was suppose to start my period on aug 12 well now here I sat almost 2 months late
Also I have been filling very tired moody and having to pee a lot and sometime like sick to my stomach I also got what look like a positive on a dollar tree test then a negative on a different one and also my nipples are sore a little bit and also I have noticed I can't really lay on my stomach as much as I did before I planned on going to the doctor on the 12 of this month witch is sep 12 2013 I have never been this late ?

There is very seldom a false positive, but false negative is very common,

Assuming you are testing with first urine of the morning, as soon as you wake up, then the tests should be valid.

I am sure you were testing for ovulation, not using online charts that do not work for many women. But that is another issue