Auto Response Texting

I am trying to create a app that automatically responses to a incoming text with the phones GPS location on a map. I have this function working however my trigger word to respond is 'ETA'. The problem that I encounter is the app will only respond once to 'ETA', then if I text 'ETA' to it again I get no response. I have the messaging set to "Receiving Always". If i reset the connection and test again it works fine once then same problem. I usually test it by texting my phone off Google voice but have tested it by texting my phone from other phones and still encounter the same problem. Any insight would be helpful, thanks.