Idk whats going on

Me and my fiance had sex and after we got done I went and went to the bathroom and I wiped and had blood on the toilet paper and so I decided to take a pregnancy test and it comes back a faint positive and we got very happy!! Then I took one 2 days later and it came back negative... By this time we are devastated!😢😢 And I'm asking y'all if anyone knows why it would come back positive when I had blood in my pee but when I didn't have blood in it it comes back negative.. Please if you have any thought please share