Hello all. First time poster here. She is a 2 1/2 year old rat terrier. 
I have noticed that when she stands on her hind legs, more of her back skin bunches up near her tail as seen in the photos. This past summer our entire housing complex had a horrible flea problem. Everyone was complaining about them and it was a nightmare to control. She was on frontline through it but even then I had to pick fleas off of her daily. So thats why her white fur is a bit reddish and her skin has a bit less hair on it towards her back end (its better under control now and starting to grow back better).

I should also mention as it said in the title that i may be overanalyzing it. I have pretty severe health anxiety myself where I constantly overanalyze my own body and health. I love her deeply so i find myself doing that with her also sometimes. This could have been the same way before and I just didnt notice it possibly. But I dont recall noticing it prior to the past couple of weeks so I wanted to ask others' opinions to rule out somwthing else or dehydration or anything like that. It mostly bunches up when she stands on her hind legs but i notice it a bit when she is sitting too. If i pinch her skin anywhere else it will pop back into place normally. Its as if she has a bit extra skin on her back than she needs or something. Any ideas or am i overanalyzing? Thanks in advance

I may be overanalyzing but my dog's skin seems a bit looser