I took a pregnancy test 2 days ago and the result was positive. the next day i took another one and it was negative. the date of intercourse 1/04/2018?

Can retest in 1 week: She can repeat a urine pregnancy test in 1 week. If the reason she did a pregnancy test is because of a missed regular period, then she can also just wait for her next monthly period... and if that period doesn't come, she can do a home pregnancy test at that time. If her monthly period comes and looks normal, no test needed. If unusual spotting or other worries, her Ob-Gyn doctor can evaluate.