So worried im not pregnant anymore!?

i took a test sunday night and it was positive...faint line but it was definitely there even my b/f saw it....so i decided i would take one monday morning so i did and the line was VERY faint still a little visible but very faint....took one this morning and again line is VERY faint...i am using early detection tests so i m thinking that i am no longer pregnant...i also feel as tho i have a yeast infection....no bleeding and AF was due yesterday....im nervouse i have a dr appt tomorrow at 345...has anyone else experienced this?