Arguing with partner post son being born, 44f and 43F. Any advice?

My partner and I have a beautiful 4 month old son who is truly joyful but my goodness has having a baby caused some arguments. We are really struggling to get a balance. I work full time, my partner is on Mat Leave. She is sleep deprived, hormonal, emotional, grieving the loss of her Mum and I am trying to spin as many plates as I can and generally hold things together. She feels I’m not doing enough and want to go out too much to exercise. I think I’m doing as much as I can in the day ( I work from home so can do a little more to help then the average person ) and feel resentful when there is push back on going out for 45 mins for a run a few times a week which keeps me fit and able to function. Anyone got any advice on how we can level this out? We tend to argue rather than communicate at the moment which is draining.