Positive result turns to negative result

Hai, i missed my period 7 days already and the next day morning, i did pt and it turns double line, and to double confirm i buy scond pt which directly tell pregnant or not and it turns out im pregnant 1-2 weeks. For the next day, i did go to see dr for ultrasound but dr said MAYBE it still unseen, so i need to go for second ultrasound in another 2 weeks. But suddenly last night, there was spotting, and i dont know whether it is period or just spotting. So to make me less nervous, i do my third pt today but sadly it turns negative which is only one line on my pt. whhhy?? Can anyone help me 😭😭😭