am I pregnant

So yesterday I took 4 test, 2 came out positive and 2 came out negative.. later that day I went to the dr and go a pee test, blood test and ultra sound and they said I was not pregnant... but if I was pregnant I would only be about 4 weeks... Can it be early effect all those test ? I've been nauseous all day don't know if it's from me being overwhelmed or what please help!