Positive then negative?

Abigail
Okay so I took an hpt yesterday and got a vvvfl. Took another one today with FMU and got another faint positive (don't have a picture since I couldn't locate my phone). I went to a clinic and they did a urine test twice and they said both were negative? It wasn't my FMU obviously and they said that might be why. But the lady at the clinic told me their tests were more sensitive than most hpts. So feeling a little bummed. I also told them I'm having light AF like cramping and they immedietly gave me info on early pregnancy loss after I told them that. Feeling a little insecure now.