claiming ITC on purchases made prior to gst registration

dear sir,
We have made purchase and sale in the months of June and July 2018 respectively,but we have registered under GST on 13th August 2018. my question is should we need to show the purchase and sale made in the months of June and July in August 2018 GST return? can we claim ITC on the purchases made in June and July 2018. kindly reply us back