Push email (Gmail) not working

Hi

I've got push gmail set up using an Exchange account on my iPhone. This is how I've always had it set up, and it's always worked, but I noticed yesterday I wasn't receiving emails and I had to open the app to fetch. I've tried turning off and on push slider, email slider, restarting phone...deleting and re-adding accounts etc. All no good.

I did a little more investigation, and strangely it appears that my email doesn't get pushed, only when the mail app is open in the background. i.e. if I close the mail app from background tasks, my emails start coming in. Once I open the app again by pressing a notification, any new emails will not get pushed again, until I close the mail app from background tasks again. Obviously this isn't ideal, as I have to remember to close the mail app from background tasks every time I check my mail.

Please help, it's driving me mad! I've always used Exchange gmail settings without any issues in the past.

Thanks