Itchy Cat due to Warm weather or food allergy? Cut on head from all the itching!

Hey everyone! We adopted a 2 year old cat in March and we love him so much but the poor guy has been in and out of the vet's office more time than I would like. He started out having major digestive issues which we knew about before adopting. He would vomit 3-4 times a day and the vets could not figure out what was wrong with hime. 2,000 dollars later, they tell me my cat is totally healthy. Luckily now his vomiting stopped since changing him from THe hills science that the vet said he had to be on for life...to a Natural Balance Limited Ingredient Duck formula. I just did not like all the added ingredients in the hills science. 

My cat started itching a lot and im not sure if it is seasonal allergies or the new food. I feel like this food is meant for cats with allergies since it is a novel protein diet. My cat has itched its head so much that it now has a large cut on its head. The vet gave him a cone and some antibiotic lotion. He also said he wanted to give it a steroid shot which i refused and benadryl. 

I like more of the holisitic/natural approach....my cat has be shot up with way too much medicine over the last 3 months and i am looking for a more practical solution. Is it common for cats to become more itchy in the warmer weather when they are indoors? His skin seems a little pink and he has violent itches where he seems like he is really uncomfortable. I am going to leave the cone on his head for a little while longer but im afraid that once i take it off...he will go back to itching it. 

Any natural treatments available for this? I heard of fish oil pills....frequent bathing....etc. I attached a picture when it first happened but now it is healing and scabbing up. 

Thanks!

I note the Natural Balance has both guar gum and carageenan.  One cat on here turned out to be allergic to guar gum, which is in almost everything.  I think you need to work on an elimination diet to discover what he's allergic to.  Check with the Cat Nutrition Forum, also search other threads having to do with food allergy.  I just had twoManxes who were turned in to one of our vets by a couple who were divorcing and didn't want them anymore and their ears were a mess -- the vet had even biopsied to see if he could find the problem. I had no idea food allergies could be that bad but just for the sake of health put them on Halo's Grain Free Spot's Stew dry and a wet food that had no guar gum or carageenan or grain and within a week they were cleared up.  It's been over a month now and no new ear problems.  Foster mom (couldn't keep them in Petco all summer and they didn't get adopted yet) is keeping to the grain free Halo and all is well.

BTW when I was clearning them up, I used something called BANIXX which is a spray/clear liquid that treats everything -- bacterial, fungal, bug bites etc. and doesn't smell or sting.  I think it helped their scratch wounds heal particularly fast.  I got it at my feed store, and of course it's available on Amazon too.

It also works on the hot spots my Siamese gets from any bug bite, and it worked on MY bug stings also.

http://banixx.com/