curtain question

[Martha-not]

ok-not baby related but I need some suggestions.
I bought very sheer curtains on a whim, but stupidly did not think about the see through factor.  Any tips on what to do?  If I hang a curtain behind the sheer, will that be too bulky?  I am seriously interior design challenged, so could use some help.  I really like the curtains, but definitely need them to be non see through for privacy reasons as well as for  keeping out the blazing sun.
Any ideas on what to do and where to go are appreciated!

thanks

[try...]

purchasing either some black-out blinds, or some nice wooden blinds, depends on your budget.

[martha not]

Thanks for the response.  Just wanted to add that the curtains are to cover sliding glass doors (leading onto balconey), so blinds wouldn't work.  This may sound really stupid, but should I put the blackout curtains behind or in front of the sheers?  I think I've seen this both ways? 
Any more ideas appreciated-I obviously need the help!