You didnt mention whether or not you are sexually active and have had unprotected sex since your last period. When was the last time you had sex?
I say this because there is a chance that the home pregnancy test was not accurate; this could be to do with the concentration of your urine at the time, how long you've been pregnant for (if you even are) etc.
Also, if you've just started your periods, they tend to be scatty and irregular. Don't stress too much - see a doctor if you're still concerned.