Sounds like September offers you a pattern of additional stress or is an anniversary reaction or contains an environmental trigger.
I sure can relate. I still don't know why certain times up my stress levels. It could even be allergy triggered/immune system based on what's in the air.
Lots of self care, lots of treating yourself to healthy but happy things, works for me. Just spoil myself rotten with sensory goodies: soft, cuddly robe, petting the pooch, cuddle a pillow, watch TV, sip green tea or water or juice...basically I treat my PTSD similar to an illness and it helps speed me through the pain faster.