Hi Kathryn,
Apologies for the delayed response.
You could pull up the referring domains report and select the referrer type as social networks, it should show them in a single line item. You may also use a filter if you want to show only the three above mentioned social networks.
If that still does not work out like you want, you may create a classification and have a custom report for the same.
Let me know if anything works out for you.
Regards,
TM