How long am I pregnant for?!

Hi there!So my periods were never regular,I had my last period on 1st of June,lasted for 2 weeks...I used to be on pill,but couldn't renew my prescription on time.(silly I know!) But anyways,I couldn't start the new pack after 7 days break...Fast forward,I never got my period in July.And since I wanted to do everything 'as it says on the box' I was patienly waiting on my period to come...Myself and my husband were very carefull everytime we had sex,using condoms,or pull out method. But on 8.08. we went out to celebrate our anniversary ,and we decided last minute to stay over night somewhere-basically, we weren't carefull enought! Few weeks later I started to feel ill,and very aware of different smells!So I took pregnancy test-which came possitive!!!!So,even thou we weren't planning we gonna have a baby!I feel good about it and all...BUT we are not sure when did it hapend???My doctor said,that in few weeks time I should go to hospital for the scans.Will that help in figuring out???Anybody had similar problem with their first baby? Thanks!