It is really important to remember, too, that it is not how long you have to stop your treatment before you get pregnant, but how long you have to stop before beginning to try to get pregnant. Once the proper amount of time passes, it's advised that you get pregnant as soon as possible.
I recommend visiting your gynecologist as soon as you start considering having a baby, so that your hormones can be tested and she can tell you what you can do to speed up conception once you have been off medication for three months (or the advised period).
It may be as simple as tracking your ovulation with a home ovulation prediction kit or strips. In some cases, if test results indicate that natural conception might take longer than is desirable, your doctor may recommend more aggressive fertility approaches, like intrauterine insemination or in-vitro fertilization.
Again, seeing your gynecologist before you even go off of your MS medication will give you plenty of time to complete the necessary tests and get used to monitoring ovulation while you're waiting for the medication to clear your body. Once the recommended time period has passed, you will have a solid plan for getting pregnant as quickly as possible.
I explain these issues in an article called Top 10 Questions About Pregnancy for Women with Multiple Sclerosis.
Good luck, and congratulations on your decision to have a baby!
By the way, it is also important that your husband or partner get his sperm tested. Many men are a little reluctant to undergo testing at first, but it is very important to determine his sperm count and quality when you are determining whether or not speedy, natural conception is a viable option.