Yes, untreated astigmatism will surely cause headache. When your eyesight is not corrected, more blood flow will be sent to the visual cortex by the brain to compensate more frequently used neurotransmitter chemicals. More flood flowing there compresses the pain sensor area of the skull and lead to headache.
Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. Astigmatism has many symptoms, while headaches is the most common one of them. Your headache also may be due to fatigue or cold. Sometimes high pressure in eyescontribute to headaches and eye pain, too.
Yes, your headaches may be caused by astigmatism because the eye nerves and brain nerves are interlinked. However, your dryness or redness of eyes from the infection at the eyes may also cause your headaches. You should protect the eyes carefully. You could use the warm compress to release the symptom. It is very workable and effective.