i have lots of experience with squints, both mine have eyesight problems and squint and yes, it is always more noticeable when they are tired or ill. what will happen is you will go and see an opthalmic optician. they do a basic eye test to evaluate, and then put drops in the eye to dilate it to have a proper look at the back of the eye. from that they can tell if he will need glasses or not. the brain has to learn to use the eyes, if one eye is not so good, it stops using it, the muscles relax, and that is when the squint occurs.
dd - eyes ok till 18mths, then one day, her left eye was squinting. she's badly long sighted in both eyes and has worn glasses ever since.
ds - referred due to dd's problems, tested at 5mths. his eyesight is fine in the right eye, but his left needs a prescription lense so he does also have glasses on that side which will pull this eye straight. he won't wear them though, just chews on them. he's too young, 10mths now so we'll try again with them at about 18mths.
they both get checked every 3 months to make sure the glasses are pulling their eyes straight. if they are still squinting with the glasses on, that is when patches would need to be used (patch the good eye for a couple of hours a day to force the bad eye to be used, this exercises the muscles in it)
there are loads of groovy glasses for kids now, so don't worry if you find out he needs them. dd has barbie ones and they do beano ones for boys!.
hope all that helps. try not to worry
. i was really upset when i found out dd needed glasses, but there are far worse things she could have had wrong with her.