Having problems with my Byetta pen's lately

I have been taking Byetta for about a year and a half now and just recently started having problems. I have not changed the way I do anything with the pen. I still refrigerate it even though I have heard that new recomendations say you can leave it at room temp after first use.  Anyway, I think lately I am not injecting anything! Usually because the byetta is refrigerated I can feel it going in as the site is slightly cold when I press down on the plunger. After I do that I count to 5 sometimes tripple that to makesure the dose should have been delivered. But lately, not only don't I feel it going in, but what appears to be a full dose spurts out of the needle when I turn the plunger to lock it before removing the needle and putting it away. The needles are obviously OK because byetta comes out of them, but instead of coming out when I press the plunger, it looks like it remains in the chamber until I tun it to lock out until the next dose. I never store the pen with the needle attached yet it ocassionaly will still form a bubble in the chamber. Any suggestions ast to why my betta is not realeasing until i turn to lock it?