One of the funniest things I see on here are the threads where guys ask "what do I do about my parents ...." finding gear, asking why they are growing so quickly, etc.
And a close second are all of these "what do I tell my grilfriend..." posts.
I teach guys how to meet and seduce women, and also off relatiobnship advice and this comes down to mainly 2 options:
1) Casual - Be in control enough of a relationship so that this is YOUR business and beyond her questions.
If the relationship is casual, your medical details are none of her business
2) Serious - If your relationship has more depth or seriousness, then be honest about what you are doing.
If it's serious then it should be serious based upon who you both are, truthfully, and that includes you telling her whats up.