Text's dont come through when connected to internet?

When connected to Internet my blackberry Q5 won't receive new texts. I have to keep opening the text chat for it to show me I have a new text. However when I reboot the handset it shows all new texts in my inbox,and then 5 minutes later I stop receiving them again. I am on giffgaff which is run on the o2 network. Please can somebody help me!