On the 3rd day of my period I let a boy put his penis inside me while I still had a tampon in. he didn't go all the way and he didn't ejaculate (I'm worried about precum). But now I am about a week before my period and I have a sore tummy (very mild) no cramps, headache and I'm burping a bit. It could be something else compeletely. Do you think I'm pregnant?

I can only say that you took a terrible chance with the tampon still in. What happened to the tapon? You should worry about precum. Please see a doctor.