As a common complaint in pregnancy, headache happens due to several causes, namely:

Hormonal changes. Estrogen and progesterone both influence the balance of neurotransmitters in the brain.

Poor sleeping habits. A disrupted sleeping pattern can affect your mood and may also cause migraines.

Low blood sugar. You may lose your appetite especially in the first trimester, but a low blood sugar can also cause headache, which will make your symptoms worse.

Dehydration. Brain tissue may lose water which will cause it to shrink, triggering pain.

Simple habits like adequate rest and relaxation, light exercise, small and frequent meals and drinking plenty of water can all keep headache at bay. Alternative therapies like acupuncture can also help.