actually, you cn have sex anytime you want, provided that:
1. you and your partner can and do both consent. see http://www.ageofconsent.com to see what's legal activity at your age.
2. you are totally ready. here's our list of things to consider when deciding if you really are ready to do the deed http://www.scarleteen.com/sexuality/readiness.html
3. you're probably tlaking about ovulating and when you can get pregnant. i'm assuming you're young. during your teens, and even into your early twenties you can have irregular cycles. this means it's very difficult to predict when you're going to be releasing an egg (in fact, even when you *do* become a regular cycler, you can still only predict when an egg is released by counting backwards from when you started bleeding).
With this in mind, we at ST never recommend that you have intercourse without a condom at any time during your cycle unless you are intentionally trying to conceive.
So what I'm saying is you can have sex at any time, so long as you always use protection. Read more about condoms, lube, and everything else here http://www.scarleteen.com/sexuality/safer.html
srm? wtf? iyhta ... rtfm!