Hann you need extra leverage. You have probably overtightened the nut.
Get someone to hold the chain whip for you whilst you undue the nut ( presume your turning it the correct way yes, anticlockwise)
I use a longer handled t bar to get mine off.
You need to go easy when your tightening them up. Torque settings will be on the nut.
So get a torque wrench and plenty of grease when you put it back on.
You should remove your sprockets frequently, also seat post and pedals, pedals even more so. If your pedals are stuck just remove the cranks and put them in a soft jaw vice.
You want park tool grease when your re fitting them