Help GS3 Won't Send Messages Periodically

[FurtimSicarius]

I have a GS3 with Metro PCS. My problem is that periodically every now and then, not too often, it wont send messages. It will remain in the sending state with the sending icon circle next to the message. I'm not sure what the problem is, any ideas on what the problem is or how to fix this?

 

[GTWalling]

Could be low signal strength.