So I have reached journeyman level of illusion and I can't seem to find a reason why the option to create frenzy spells is not available. Do I need to be an expert or master? UESP isn't being very helpful with this issue. Any help will be much appreciated.

Do you know the spell? You can only create spells if you know the spell effect. You can buy the cheapest version of the spell form Delphine Jend in Bravil.

Do you already have a frenzy spell in your spellbook that you can cast? If you have an expert/master level frenzy spell,but not a Journeyman(or lower) one, you cannot use it to create spells. Or at least that's what I've heard.

No, as far as I know I do not have any frenzie spells that I am able to cast. So if I buy any frenzie spell I can create a new one regardless of the level of the spell? Thank you all for the responses by the way.

As long as you know the spell effect, you can create spells up to your ability to cast them. So you can buy a cheap novice frenzy spell, and then create a Journeyman level version of it. More importantly, you can combine the frenzy effect with some other spell effect; that's the beauty of custom-made spells.

For instance, one might create a spell that cast frenzy on target and invisibility on self, to prevent the frenzied individual from attacking oneself.

Really, I didn't know that. I'll experiment with that. Thank you for your help.

Yep, you have to know the spell and be able to cast it. If you picked up a Master Frenzy spell you wouldn't be able to create anything with it until you could actually cast it.