Please help asap!

I try to copy and paste an existing formula into a cell bellow it and it is acting like it is auto filling rather than copying my info. For Instance I copy cell 2 (='2'!B3+'2'!B4) into cell 3 and it changes the cell number rather than keeping it exactly the same. Please see below for example.

='1'!B3+'1'!B4
='2'!B3+'2'!B4
='2'!B4+'2'!B5

Another problem I have is that I need to copy the exact cells down 31 lines and just the worksheet number change and I cant get that to work either. When it auto fills it adjusts the colum number and not the page number. I have to get this done by Monday for work and I am about to break my computer!

Exp.

='1'!B3+'1'!B4
='2'!B3+'2'!B4
='3'!B3+'3'!B4


Please help me out. Thanks