False positive or false negative?????

Hi I am borrowing my friends log on and I just wanted some advise on false positives! I have posted on TTC aswell just to get some much needed help.

I have taken 3 tests and 2 have had a faint line and one was neg!!! I do have a n appointment with the Doc to do a blood test but I just wanted some advise before going.

Is there such thing as a false positive????? or have I had a false negative??

Please help

Orla xx