i have this problem where my gas needle keeps fluxuating like if i have my gas tank is empty but when i add 30 dollars worth of gas it says its full and if i buy 50 dollars worth it says it full also but they go down at different speed. Also the needle doesn't go down when I turn of the car and when i go to my car later the needle is lower then I left.

IT sound like your fuel sending unit is bad which is located under your rear seat. Mine was doing the same thing and i replace my whole fuel assembly and it works now. You can check withh your local salvage or used parts store as i did and was able to get a used one for 60 bucks very reasonable, and love to have my gauge back.

remeber though its a gamble to buy parts like this from a salvage yard. especially parts that have been sitting in old gas for months or years.