Did the NUCCA rate the amount of misalignment in your Atlas ? A single NUCCA treatment is just the start. You want to achieve stability of Atlas. You should be icing after each treatment.

The Declofenac is an anti-inflammatory med. If you do not notice any problematic side-effects, it may be worthwhile for a week or two, maybe more to see if your neck stabilizes.

Delayed headache after exercise does not make sense. Do you have a blood pressure kit ? It would be interesting to see if your blood pressure has a pattern that matches your headaches. I believe everybody should have a blood pressure kit at home. You can buy them for as little as $15 to $20 for a wrist model.

Dehydration can lead to headaches. When I get a headache, I have learned to drink a glass of water. It usually helps but it makes my tinnitus worse.