My dog has been acting strange

Hi everyone! It's been a while since I posted on here, hope everyone is doing well!

My dog Sydney has been acting weird for the last 3 days and I can not pin point what it is.
Usually when Syd has an upset stomach she makes this groaning type noise and then I let her outside and she eats a bunch of grass and then she is fine...however about three days ago she started making this noise so at first I thought she had an upset stomach, but then I noticed she would make the noise and start running around with her butt and tail to the side, lay down,get up, make the noise. It does not seem to be an upset stomach, she will do this for like 5 min, then she is fine for a while, playing with my new puppy, eating,swimming,napping, and then she will do it again.

I was thinking maybe she has a bladder infection, but then she isnt peeing a lot or licking herself, I also thought maybe she needed her anal glands expressed, but again she isnt scooting or licking that area either....its just this weird noise like she is uncomfortable with her walking around funny.

Any ideas?
She does not seem sick otherwise, like I said she is playing all day and being normal other then for these 5 minute periods that happen randomly throughtout the day.
(sorry for the typos, I'm still waking up)

Thanks for any input!