Session Retain problem once form submit and return back to pervious form

["sridhar_vpy" <sridhar_vpy@xxxxxxxxxxx>]

I have a 4 forms,each form value to store on session while i submit that form using submit button,Once i click back button on the each form it go previous form in that form it self click next button from first form itself,The values are destroy what appear in the form and also resubmit the page again.Also i have link name change in the 4th form if i click that link it will go to second form in that second i click next button the 1st form value what i store in session are destroy. What exact problem 
in the 4th form i use link
<a href='/fwdphp/categories.php?a=$val1'>Change</a>