Gas Gauge Issue!
 

I have a 2012 Mazda 2 with 98k miles. Recently, the miles until empty gauge seems to be funny. I will leave my house with 50 miles remaining, and not having even gone 3 miles the gauge gets down to 28 miles remaining. What could cause this? I have no clue how many actual miles I have until empty now because it jumps so drastically within minutes.

How long have you had the car?
How long has this been happening for?
Do you always fill the tank to the top/full?
Has it started using more fuel than before/normal?

I've had it for 4 years, bought like new with 2k miles. It's been happening for about 2 weeks. I usually always fill it up full. It has seemed to use more fuel than normal.