Why is my 2001 honda civic loosing coolant?

I have a 2001 honda civic Ex 1.7L. It is rapidly loosing coolant and I have no idea why. I have taken it to 3 professionally owned shops for the same reason and all three can't find anything wrong with it as far as leaks. My next best guess is that it is burning it somehow but I can't think of why. I did buy a new radiator cap and ill see how that works and there isn't any white smoke coming out of the exhaust so I don't think it is the head gasket.

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If the coolant is not leaking externally, obviously the block is cracked, the head is cracked, or you have a bad head gasket.