Headaches are common in the young (and older) adult population. They often come on in the teenage years and parents are not sure if they are stress or hormone related or due to the fairly universally poor sleeping habits of adolescents. Some worry that they are a sign of something more serious underlying.
Most commonly in 13 year olds I would say are the tension type headaches and migrainous headaches, followed by headaches caused by things like sinusitis.
Tension headaches usually get worse towards the end of the day or when tired. It is a squeezing type pain on both sides of the head, around about the temples or in the front of the head. There are no added features like nausea or seeing bright, flashing lights but there can be associated light sensitivity. Paracetamol or non-steroidals such as ibuprofen work fairly well for this type of headache.
Migraine often runs in families and you may recognise some of the symptoms in your son if you are a sufferer yourself. The pain is often described as throbbing and is more severe than with a tension headache and the young person usually feels better if lying down in a quiet, dark room. They may feel nauseous with it and may get an aura (warning) beforehand consisting of flashing lights or blind spots. If he is not getting very many then pain relievers as above may be the most appropriate management but there are a number of different preventative medicines for people whose life is severely affected by frequent migraines. In about 20% of cases certain foods can make migraines worse eg. chocolate, coffee, oranges, cheese.
Sinusitis can cause headaches; does he have a blocked nose? Dark rings under his eyes? Pain on pressing above the eyebrows or under the eyes or on moving his eyes from side to side? Sometimes antibiotics are needed to clear up a bout of sinusitis.
The sort of things that should make you take him to the doctor straight away are pain which wakes him up at night, sudden severe pain (sometimes called “thunderclap” pain), weakness or numbness down one side of his body, on-going slurred speech or double vision, headache on coughing or laughing and any change in behaviour.
https://www.nice.org.uk/guidance/cg150/resources/headaches-pdf-243935625157: parent and young person information on tension headaches, cluster headaches and migraine.