I'm sorry about your BFN.
I'm just dashing out the door so not a lot time to write, but I've seen ladies on this board POAS and get a BFN.....only to get their betas and have a BFP. Sometimes it just doesn't show up in urine.
Please please please stay on your meds and get your beta. I know it's tough to hear those words over the phone if it does turn out to be a BFN, but rather be safe then sorry.