Becca: My answer is somewhat dependent on your age/stage in life.
If you are in grade/high school, living with your parents, I say:
Maybe start working on getting your parents accustomed to the idea of you being an LGBT ally (see previous post). Obviously it’s your choice whether or not to come out, but you’ll probably want to eventually. As for the no-boyfriend-thing, tell your parents that you’re young and want to focus on yourself. You’re not looking to date just for the sake of dating, and you’re willing to wait for the right person. (not 100% forthcoming, but it should get them off your back).
If you are a young adult (College, 20s, whatever) and partially independent, I say:
Tell your parents that you’re young. Right now you want to focus on yourself, your career, making strong friendships and figuring out what you want to do with your life. Tell them despite their encouragement, you are not just going to start dating any old person for the sake of having a boyfriend. When you meet the right person, it’ll happen.
If you are older and fully dependent:
First, to really get them off your back, you could tell them flat out. They may be shocked, angry, hurt, repelled, but hopefully knowing that you- their beloved daughter/sister/cousin-a real person, are a lesbian, they might come around. I know some people’s upbringing and religious beliefs make it difficult for them to get past their homophobia, but the harsh truth, in my opinion, is that if these people can’t view LGBT folk as equal human beings, they might be better off with less involvement in your life, family or not.
If you’d rather maintain your discretion, tell them that your romantic relationships are your affair, and you’ll tell them about/introduce them to your romantic partners when/if it should reach that stage and you’re comfortable doing so. They’ll simply have to accept that you’re an adult and they don’t get to be privy to your every date and relationship.
Good luck, as always.