I had a baby on 4 December,2011. Now my baby is 2 months old, in between we had intercourse n I went to my lady docter but she told me to wait for the next date, I'm afraid that I'll b pregnant if I'll wait for my menstruation date, what should I do to prevent pregnancy now?

Have your periods returned? If you are exclusively breastfeeding and your periods are not back, then it's very unlikely you'll get pregnant.

If not, then consider using condoms until you talk to your doctor and find another form of contraception.

You already had sex and I assume non protected, so you can't close the barn door after the horse is already gone ( so to speak) If that act of sex made you pregnant then you are. Did you tell the doctor you had sex so early after giving birth, there are other dangers of infection and harm to you, that can happen.

Next you just don't have sex for a while, or use condoms till the doctor will start you on other birth control.