Trouble with face masks

On Monday face masks became mandatory on public transport and in small spaces. I have tried wearing a face mask but really struggle with it. Partly it is the feel of my own breath on my face and the dampness of it, as well as the scratchy material behind the ears. But I can barely wear a face covering for twenty seconds before I have to take it off. Strangely it's the fact that my nose and mouth are covered and I have to breathe through those, but having the mask there makes me think that I can't breathe (sorry if that sentence makes no sense).

I know certain people are exempt from face coverings, including those with a "physical or mental illness or impairment". But I'm only mildly autistic and nobody would even guess that I'm autistic unless I told them, so I fear that if I didn't wear a face mask I would get penalised for it. Also I hate thinking of autism as a mental illness.

Anyone else struggling with face masks, or have any tips for coping with them? I have to take a train to the hospital next Friday and I'm truly dreading the journey.