It is common knowledge that when you share your data connection via personal hotspot there is significant battery drain. There is little to nothing that you can do about that.
Second, so you have wifi on, then you turn on personal hotspot? When you do that it doesn't do anything it just thinks?
Try a reset, hold home/sleep buttons until the device powers down and then powers up and you see the apple logo. Release the buttons only once the apple logo appears, then try again.
I never had any issues until I upgraded to software 6. I never had to mess with the cellular data button. I don't even use the personal hotspot. So I'm just trying to figure out when I have the WiFi button on and the cellular data button my battery drains fast. I've been trying to figure out if something else is running but no luck.
So, you're actually confusing me a bit.
You have an iPhone, with a data plan? If so you need to have cellular data on to use your cellular data plan. Next, when you're using wifi (with cellular data still on) the device will reduce the use of cellular antenna and should save battery.
As far as battery conservation, turn off location services, turn off push email/notifications, ensure bluetooth is off when not in use, and see www.apple.com/batteries