Tampon/ birth control

I started my period 4 days ago. And yesterday I started my birth control (pill). I don't remember if I put in a tampon after I. Got out of the shower but I don't feel a string for the tampon... I haven't bleed all day and I'm not sure if my tampon is way up there or if my period stopped because of the birth control like my doctor said. Any suggestions?  Besides going to the doctors.