Headaches can be caused by lots of stuff. Migraine can be triggered by lots of stuff. I don't see why cancer (the particular kind your husband is dealing with, the treatment, or even just the stress) can't be a possible cause. Unfortunately that doesn't make the pain go away...

I started getting migraine-type headaches after my daughter was born. It's actually common for those lovely pregnancy hormones to reset our bodies to weird new normals. I figured having daughter would give me headaches in her teen years, not that early, LOL. But it's been 'me' now for a pretty long time. I've got lots of triggers, including stress and environmental factors, but that's the closest to a 'flipping the switch' event that I can pinpoint. (Clearly not his issue!) Since it IS migraine, though, that opens up different medication options. Some help, some not. But it's worth asking ... are they treating it as just pain, or as migraine? (if that's what it is) Worth checking into. Also, nerve pain has different options from muscle pain, and so on. Again, some work better for some folks than others ... but it can be worth asking about. All those nerves getting affected by treatment, stress, whatever ... they can cause 'referred pain' where it hurts in a different location from the actual source. That's a trial-and-error sort of discovery with treatment, but if it helps, go for it. (The stuff like gabapentin seems to be the first medicine prescribed in those situations, nerve pain ... works great for some, just have to watch side effects.)

Random thoughts, but maybe something in there would help. Hope pain relief comes soon! ((hugs))