Gas guage not reading

Today I cranked up my car without pressing the gas. It started and ran fine and quiet all the way home, which is an 18 mi drive, but my car said I was on E! I had put $20 in yesterday and the gauge read that fine. Now, today I went to the gas station to see if I really was riding on a dry tank and so I cranked it up while pressing the gas to go to the gas station. It gauge read, but about 30 seconds later, the gauge went back to E. I think this could have a problem with my oil sending unit, because it is leaking. Any advice?