weird gas problems on 2001 toyota corolla

ill preface this by saying, I bought a 2001 Toyota corolla a month or so ago that now currently has 156k miles. it runs great, but there is a problem with the gas gauge / lines? first problem is a big one and it just started yesterday, the car only will take around a gallon of gas at a time before the pump clicks off. and yes, this is when the car was at half full or less. and, i tried two different pumps at two different stations. the reason I'm not sure the exact fuel level is because it appears as if the gas gauge is faulty as well. it had 200 on the tripometer and the needle was at the half way mark. no way it got 40 mpg, I calculated it as getting barely 30 the week before. also, yesterday I managed to put around 4 or 5 gallons in it with no visible overflow of the tank, now the gauge says its full. drove today 60 miles and the needle is moving slightly but then it goes back up to the top of the gauge indicating the tank is full when it clearly is not. any theories as to what might cause this?