I'm not on HRT either, but I have been trying numerous combined pills for my peri symptoms. My latest pill gave me exactly that - calf cramps. They were worse the first few weeks butbthen settled down.
I never get cramps either - exveot I remember having them when pregnant. So defo the hormones.
I agree, it is a worrying side affect. The pill that was causing it for me is the one most closely linked with clots - so it was worrying. For other reasons, I've had to stop it.
If it continues to bother you, maybe change to a different type. X