My girlfriend might be pregnant?

CC

So I don't have any pictures or anything, but we're in an open relationship and on Friday the 13th she thought it would be fun to have sex with a guy, which i obviously said yes to. Fast forward to now, she's constantly nauseous and super sensitive to smell. Period was supposed to start two days ago, took three tests in the past week. First test was negative, second was a weird faint line, third was negative. We are thinking maybe a blood test? Any similar experiences? We've been having a lot of baby dreams lately and we both think it's a religious sign (sorry to bring that into this but I think its important to mention) but so far we don't really have enough confirmation. Help!