pitbull in heat

Question
my dog is in heat! but the guy i got her from said she was only 7 months! but a week after i got her she came in heat! i don't know if he lied to me and she is older thin that?

Answer
Seven months is about the earliest they ever come in heat.  This is part of the reason it is common to spay them by 6 months.  Your are stuck with going through it now.  Few vets will tackle the complicastions of doing until the heat cycle is all over.  

The second and third weeks are when the most risk of accidental breeding is. Don't take this lightly. She will do anything to get loose and get to a male. Once loose, an accidental breeding and an unwanted litter is far from the worst that can happen. Such breedings can also result in fatal infections. She can get killed when she dashes heedlessly across the road in front of a car. Other dogs or coyotes may kill her.

I hope you planning on spaying her.  You can expect the same thing about every 6 months for the rest of her life if you don't go ahead and get her spayed. There is no other answer, and no good reason not to. Besides saving the hassles, it reduces the chances of cancer later in life. Please make life easier for yourself, her, and society in general by getting her spayed as soon as a vet will do it.