There can be a number of things that can cause this sensation: dry/irritated eyes (very common), headaches (including migraines), inflammation behind the eye (uncommon), inflammation in the eye (not very common), and even glaucoma (quite uncommon).
Dry eyes can cause burning, irritation, a foreign-body sensation, achy pressure, sharp stabbing pains. It does typically manifest later on in the day after we've used our eyes a fair amount, moreso than in the morning, but there is a type of dry eye that can be worse in the morning.
Migraines tend to be accompanied by nausea, sensitivity to bright lights or loud noises and some kind of visual phenomena usually described as shimmering lights variably around spots you don't see well through in the vision. Run of the mill tension headaches can produce these as well.
Inflammation behind the eye and inside the eye would be accompanied by a significantly red eye and sensitivity to light. Glaucoma causing this type of pain would either be associated with intense pain and nausea/vomiting or halos around lights. None of these things are common though.
Dry eyes are the most likely cause. I would start by using artificial tears, 4x/day in both eyes. But the key to using these is they must be consistently used in a scheduled fashion for them to work. And they must be used 4x/day, daily for a few weeks (3-4 weeks) before you can know if this is going to help and if dry eyes may be a cause. When you use artificial tears only when you feel like you need them then they only last a few seconds (the effect) and does nothing to change the overall course of the problem. I would also recommend using cool compresses. You may also consider using tylenol or advil with this pain to augment the lubrication to see if this helps.
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Thank you so much. I will try the artificial tears firstly. I don't get any pain or stabbing pains, but sometimes my eye feels like it is pulsating like a heartbeat.
I don't know what Tylenol is or Advil as I am from the UK and not heard of them.
Cool compresses then, not warm ones?
Cool compresses can help with discomfort. For a certain type of dry eye that stems from inflammation in the eyelids, then hot compresses in the morning for 5-10 minutes on a daily basis helps to treat that. Sorry about using the brand names. Tylenol is acetaminophen and Advil is ibuprofen.
Hope that helps!