There are couple of reasons which can led to that. Looking at your smartphone it is perfect for using 3G internet as it is supports most of the 3G bands. It seems that there are issues from your back-end side (Network). So, here are few steps which will help you to resolve your issues.
1. Download proper Internet Settings as per your Carrier. You can call to your customer services and let them know about your issues. They will send you internet setting capable to run 3G internet.
2. I know its silly but make sure that there is 3G internet available on your phone and its not 2G. You can't use 3G speed internet on 2G recharge.
3. There are signal issues with some of network providers out there. If you are using Reliance then it is normal there connection drops most of the time. Not criticizing but there are many other mobile operators which have issues of connection drops.
4. Please check with customer service if 3G is available at your place or not.
5. If none of them works then please try to check with any another mobile operator, if its working or not and if it succeeds then I will prefer you to port to that operator.
I am currently pursuing High School and planning to pursue career in Computer. Currently, I work on one of my blog - JTech Articles.