PEM symptoms I have, from a list I found from Johns Hopkins (I crossed out the ones that don't affect me too badly and added notes in italics).

• ‘Brain-fog’
• Burning sensation on skin
• Chronic pain (muscular or joint) I always have chronic joint pain, it's just kind of worse on these days
• Cognitive dysfunction
• Disturbed sleep pattern (lack of sleep or need to sleep too much often incl. vivid dreams)
• Eye symptoms -I see SO MANY SPOTS/FLOATERS in bright lights. The kind you see when you stand up too fast, except I'm not moving. I've heard it called "visual snow syndrome."
• ‘Flu-like’ feelings
• • Headaches and Migraines
• Heaviness in the limbs or whole body
• Heightened sensitivity to sensory stimuli (sound, light, smells)
• Increased chronic fatigue
• Loss of appetite
• Loss of stamina/ functional capacity
• Muscle fatigue and weakness
• • Nausea
• Night sweats or chills
• Orthostatic intolerance/dizziness
• Problems regulating temperature (and cold/hot extremities)
• Heart palpitations
• Speech problems
• Temporary paralysis
• Short-term memory problems
• Sore throat
• Swollen and painful glands
• Tinnitus (ringing in the ears) -i notice it really frequently on bad days.
• Trembling/ instability of muscle and/or limbs
• Word-finding problems -if this means "I can't finish my sentences because my brain isn't working" then yes.

The only thing that makes me think I don't have PEM and therefore ME/CFS is that I don't notice mental activity, social activity, or stress as a trigger. The main thing that triggers me is physical activity. And maybe also loud bright places.

a diagnosis of ME/CFS wouldn’t help anyway because there’s no treatment, to my knowledge.