So you can't make a cure poison potions in Skyrim, only buy them?

I chose to keep my werewolf blood and therefor stay immune to all poisons. I never tramsform into a werewolf.

Are you immune to poison as a werewolf? I thought you are immune to disease, not poison.
You get poison immunity as
OP - no, there are no ingredients that have cure poison effects, so you cannot create a "Cure Poison" potion. Only Resist Poison.

I've never met a poison in the game that needed to be cured.

Yeah, you can only buy them but they're pretty rare to find in alchemist' inventory, I come across most of them on the road. Honestly, so few enemies use poisons that it's really not worth worrying yourself over. The most common poison you're likely to run across is from Frostbite Spiders and sometimes the Falmer coat their weapons with weak poisons, but it's usually a one-hit-use potion and the ones that have dots are almost never significant enough to warrant curing yourself.