Learn English – the expression for saying grateful

First off, I think that the verb to count doesn't work well in the context of making mathematicalензщ calculations using your intellectual ability, in other words--solving math problems mentally. The process may also be reffered to as "mental maths" or mental arithmetic that is doing calculations in your mind, without writing down any numbers. If you google for "calculate mentally" or "mentally calculate", you'll find lots of examples.

Also, see the " in one's head" phrase which in your case hits the bull's eye, as Tromano pointed out in his comment:

He was great with math and could give you batting averages calculated in his head. (the source)

Different forms of discomfort.

Hurt is the usual sharp pain as from injury.

Ache is a dull pain, usually internal. With migraine, your head aches, but if you bump your head on a door frame, it hurts.

Soreness is either an ache that appears 'when moving' - e.g. muscle ache after intense exercise, or a several days old bruise or an itchy form, like 'sore throat' - not yet hurting but with 'scratching' feeling.

There's throbbing pain, e.g. during intense migraine, where the intensity changes with your heartbeat, each pulse of blood sending extra pain wave.

There are pangs (of pain) - intense waves. Birth pain is definitely this form.

There's burning - not just from getting burned; strong reflux causes burning, so does very spicy food.

Something smarts when the pain is pretty strong but short-timed. A fresh minor bruise, a paper cut on your finger, kicking a table leg with your toe, that all smarts.

There's chafing - pain from repeated rubbing; result of badly fit shoes, some kind of belt or strap rubbing against your skin, possibly causing inflammation. It makes the place tender or sore.

And the very extreme, agony - a completely crippling, excruciating, overwhelmingly intense pain.

If you remember any more, just add and I'll try to add.