Downloading iMessages on MacBook Interrupted

I opened my Mac after months of not using it to see whether my imessages were coming up on my computer as well. When I opened the messages app it started downloading all of my messages. While downloading I sent a message from my Mac to a friend.The download immediately stopped and hasn't continued. I am getting the new messages my friends are sending but there is a gap between the date that it stopped the download on (May 28th) and today. So all the messages from May 28th till now are no longer downloading.. How can I get it to continue downloading.