iphone 4 - saying I have messages when I don't

I deleted a few messages I had already read. They were from one person only, and it was a bit of a long thread. Now it's saying I have 11 unread messages, when I have no unread messages. New ones will appear as normal, and when I read them the number goes back to 11. I've tried resetting my network settings, I've tried the most popular solutions I've seen online, and none of them have worked. Sometimes the number will disappear, but when I open the iMessage app again, the number returns. I have the latest version of iOS 7.0.4, and this problem started happening maybe a week or so after I updated. I have had no other problems so far. Down below is a screenshot of what's been happening. Any help would be much appreciated.

Also, when I get more messages from this person, the same person, the number doesn't go away either.

http://i40.tinypic.com/2rzyiie.jpg