Positive result that disappeared

Samantha • I am about to be 30 years old. I have a little boy who is my pride and joy. I was told I would not be ever to have a child naturally so he was a huge surprise and my miracle.
I have taken now 2 test. I have a very irregular cycle and one fallopian tube. I see a infertility Doctor for the first time on Monday. I have been having symptoms of pregnancy but when I take a pregnant test it shows positive faint line then it just disappears. I should start my period on Friday but hoping I dont. Has anyone experienced a test that has a faint line then it just disappears?