Sorry but it's not enough information just to know the length
of a side.  Look at these two rhombuses below.  Both have the 
same lengths of sides.  You can easily see that the diagonals
(in green) of the one on the left are different from the lengths
of the diagonals on the right:



What information did you leave out?  If you like you can put
the information that you omitted in the thank you note form
below and I'll get back to you by email.  No charge ever.  I
do this for fun.

Edwin