She may well be going into heat - every bitch is different and some do have a first season before they are 6 months old. Get the vet to check her in case she has an infection or other problem that needs treating.

When she does go into season you will have to be very careful even when you are with her - she will be as keen to get to dogs as dogs are to get to her!! That urge will overtake any training or bond that you usually have with her.

It is a sad thing to say but the last thing the world needs is more puppies - and for your bitch's health the sooner you can have spayed after her season is over and blood flow is back to normal the better.
I'm not trying to be nasty in any way but it may be a safer bet to have this bitch as a companion and to learn from before you decide if you are up to breeding as well. It is hard work, messy, can be dangerous for Mum and pups, is costly and emtionally exhausting - and that's just the first bit! Enjoy this bitch and learn from her before making the VERY huge jump to puppies.