Why can't I connect to the internet when I'm out.

My alcatel one touch pop icon will not connect to the internet when I'm out. I can only get it if I'm at a location with wifi (and sometimes won't work there). Before I began having issues with this phone I could go practically anywhere and still have internet connection by just having my data connection on and my wifi but that no longer works. I really do need this feature of being able to access the internet from my phone. Any suggestions on how I can solve this issue?