Since cluster headaches are seasonal then surely it must be related an allergic reaction of sorts...exhausted?

Possible: Historically, called histamine cephalgia, but not really clear that these are allergy related, but often seasonal and perhaps due to susceptibility factors. You can stop these with preventative measures, and consider steroids, depakote, topamax, (topiramate) naproxen, even lithium. Otc perhaps butterbur, feverfew, riboflavin, co-q10. Can often stop these by breathing 100% oxygen. Talk to your headache doc.

Not always: Cluster headaches can be severe and frequently the trigger is elusive. While allergies can lead to nasal symptoms, fatigue and disrupted sleep, the role they have in triggering is difficult to assess. If treatment for allergies improves the headache, this can be indirect evidence. If not, see a headache specialist.