19G data this month already. should I be worried.

[18wheeler]

With SERO unlimited data I figured I could tether my TP2 to my home network through a DD-WRT router, since I am the only one using the internet at home.

I just checked this month data usage, it is already over 19.3GB with 19 days left in the billing cycle. I am truly shocked by the number. between my computer and iPad, I surf net, check email, etc. for 2-3 hours each day. occasionally watch a few youtube videos (10-30 minutes on average). Never download large movie files etc. the largest file I downloaded for last month was a TP2 rom. How come the number stacks up so fast?

Now I am worried Sprint might argue that I have used too much data, questioning if I am tethering, and send me a large bill.

Am I paranoid? How do I defend my self IF Sprint does something?