Why won't my iPhone 4S go on the internet outside of a Wi-Fi zone?

So I have a two year old iPhone 4S and live in turkey. We went to the states in summer, in which I had to turn off my cellular data and stuff so I don't get charged, when we came back, I turned all of it back on, but whenever I leave my house, I can't go on Instagram or twitter or anything. Why does this happen and how can I change it? This has been going on for two to three months

Talk to your cellular operator. Make sure you have cellular data turned on for the apps you want to use.