I just noticed that there is no difference between form1, form2 and form3 other than the value 1, 2, or 3. So you might pass these on to the form in the url.
<a href="form.php?formnbr=1">Form 1</a>
Then in form.php get the form number and place it into the form
<input type="hidden" name="formnbr" value="<?php echo ISSET($_REQUEST["formnbr"]) ? $_REQUEST["formnbr"] : 1; ?>">
If you are not familiar with the construct I used in that the expression
x = a ? b : c
will evaluate a and if true return b and if not true will return c
is the same as
if (a) { x = b; } else { x=c; }