1 week late & 2nd line still so faint - HELP

Please help girls, we have been ttc for 18 long months & I am going out my mind. My period is now a week late. I took a test Wednesday & it was a faint positive. I have managed to hold out until today to take another test & still line is faint. Should there not be line progression? Do u think I am pregnant or could the faint line indicate a problem coz a week late? Thanks so much x