I have filed an application under RTI but 2 days after filing my application, now I want to get some more information. Is it possible to get the new information also under the same application OR do I need to file a fresh application ?
As I interpret you left some issues, thus asking through a new application would not affect the issue of 'same subject'.
How much is the application fees you paid, and who is the public authority? As there is no provision in the act I had come across wherein you can ask for supplementary questions into the original one, I interpret the act by suggesting you to apply for new application, preferably not including the original questions you had asked, but the reference to it.
You can ask in a new application to club them for reply purpose, and as you asked in a new thread, your application is bound to be treated as an application and would not be rejected.
Each application under RTI is treated as separately. Other wise the period of limitation is difficult to calculate.
As kushal suggested you can file a fresh application under RTI mentioning the earlier one.