Engine light on

My engine light has been on for just under one week and for the past 1 and a half days my gas meter arrow has stayed in the same spot even though I have been driving my car and clearly using gas. This is the first time that I have had this problem. Obviously my car is old so I understand that issues may come up but I have no knowledge of cars. Is there anyway to know what this may be? Everything else is working fine.

My car has 119000 miles.
My car has an automatic transmission.

– Engine light on