How to design the primer when you don't have GC?
Without the sequence information I can only give very general advice. 

1) Pick a different location — primers generally work best when they have something close to 50% GC content.

2) Make sure the 3' ends of your primers aren't complementary.

There is detailed advice on how to design effective primers available online including:


from MIT
Dieffenbach, C. W., Lowe, T. M., &amp; Dveksler, G. S. (1993). General concepts for PCR primer design. PCR methods appl, 3(3), S30-S37.