2001 Dodge stratus fuel pump problem

We are having a problem with our fuel pump,we think.We have to bang on the gas tank to start it ,but then after it starts we can drive it and if you turn it off for a minute it will start again ,for as many times as you want,but then if you wait overnight you can't get it to start in the morning,and we have to bang on it again,is it the fuel pump or something less expensive?:frown: