Helmet suddenly causes pain .. ?

Hello everyone, I’ve been riding a Shoei XR-1000 helmet in size M for over 4 years. It’s been great for me so far, but since this year it’s been pushing me so hard on the right temples that I get headaches and toothaches if I keep it longer. As soon as I put off the helmet, however, the pain is immediately gone. The joke is that I do a bigger tour with friends once a year, that I can take the helmet up to 10 hours in places. I’ve never had any problems with that! Well, I’ve assumed that the helmet may have just become too old, e.g., and I ordered a new one – a Shark RSR2 in size M. I had already worn such a helmet for my mother’s rehearsal (was a gift for her, 2 years ago) – and that’s where it fit me brilliantly. But about half an hour later this helmet is also making me create! Same symptoms as with my Shoei, ever but with pressure on the ears and on the jaw bones underneath, which also results in headaches, which disappear as soon as I have dropped off the helmet. So I ordered another one for comparison – an Arai RX-7 in size M, because Arai helmets always fit me very well when trying on. Missing!!! Also after half an hour so nasty that I get pain. Some will now say, I should try Size L – but the Can’t be, it fit me ALWAYS size M! Only since this year it’s mysteriously not anymore…. Besides, I tried Size L at least at Arai in the store, was clearly too big, wobbled and creaked. Can my head have changed like this???? What else can this have for reasons? My hairstyle hasn’t changed since I bought the XR-1000 back then. Does any of you know this phenomenon? Any tips on what it might be and what I could do? H Help. 🙁 Thank you!