Irregular period and due date confusion!!

My last period was April 10th I didn't see my period may so decided to take home PT on 5th june which came out negative a month later I started feeling funny then I took another home PT on July 4th this time positive. My husband then took me to our doctor to confirm it,after explaining to him he ask me to go for a scan which due date is 21 Feb 16 but my midwife said it should be 17th Jan 16 instead I'm confuse I don't which one is more accurate. should I go for another scan in a different place? I'm 22weeks 5days today