5 MB is literally nothing. Opening Haaretz.com *once* is more than 1 MB. I’d go through 5 MB in an hour, I estimate, on my phone – without ever watching videos or making VoIP calls! I think you must be mistaken, it has to be 5 GB. I cannot believe 5 MB data plans exist!
Also, I recommend the default browser instead of Opera; personally I only find Opera difficult and annoying.
And most of all – congratulations for choosing Nokia as opposed to what most other people get! I’m a big Nokia fan and have a Nokia E72, with unlimited data.