Positive test then negatives

Monday I took a first response at night and got a faint line. I even posted it on here and got 12 comments saying yes and that others saw it! It was super faint so I went to the clinic to try to do a blood test and when I got there they said they’d just do urine. I took a dollar store test less than an hour later and it was negative. I still felt like I could be pregnant because af is over a week late and I thought maybe since I took them so close it wasn’t concentrated enough. Well 2 days later I took another and negative. I’m so confused. I still haven’t gotten my period this is the longest I’ve ever been late. Has this happens to anyone else?