Why is my dog swollen back there

I bought my daughter a pitbull off of a friend about a year ago. The only reason I got her was because I wasn't planning on breeding. The dog was born with her vigina and butthole to close together which was not a problem. I couldn't help but notice that the dog is looking alittle swellen back there and I don't know why. I know dogs swell up when they get there periods but she's only a year old and I think it's to soon. Could you please tell me what wrong and if I should take her to the vet.
   

She's probably in heat dogs can go into heat as early as 6 months of age but that depends on the dog. If you are not planning on breeding her i would get her spayed.

My mixed Yorkie,Chihuhua and Jack Russell, his back looks somewhat swollen. It's not flat like usual, and i think when he jumped off the bed it may have affected it, but he can walk, but not very well, he walks a few steps then he sits. Hes still eating and drinking. Once before he jumped off the bed and hurt his back leg and couldn't hardly walk for about a week, than it healed up, this was around six months ago. Now im not sure if he hurt himself again by jumping off the bed or not, but it's just my guess. His back may be fine and it may be his leg again hurt, but to me it looks like his back is somewhat swollen. What are your Suggestions?