False positive pregnancy test?

I’m 14 weeks post partum. I have had my first period around 7-8 weeks postpartum. I have been feeling extremely nauseous, dizzy spells, missed period and am soo tired. I have taken a few tests. I’ve had 1 faint positive yesterday and one negative and then another one today is negative? Is it possible to have a false positive or is it more likely the other two tests just aren’t picking it up? I’ve got a few more to do in a few days. This is the faint positive yesterday after reading the test straight away after the specified time.