Vomiting Cat question

After purchasing Scentsy my 2 year old cat started vomiting every night.  It started out clear but over a few days became pink.  I had been using the Scentsy in that particular area of the house.  We didn't think about that being a problem.  After about a week it started to happen during the day as well.  One day we gave him some tuna because he hadn't been eating well.  He vomited it up within 5 minutes of eating it and then again about an hour later after eating some dry food.  I had my husband take him to the vet.

After running test she found that his protein and albumen was low.  She also said that the beginning of his intestine was thicker than it should.  I have those x-ray images if anyone is interested.  She gave him a shot to keep him from vomiting for 24 hours and an appetite stimulant.

We brought him home and he was fine for 4 days.  I started using the Scentsy again since our life was seemingly back to normal.  He began vomiting again which is when we decided that perhaps the Scentsy was part of the problem.  He had stopped eating and would sleep most of the day.  So we shut off the Scentsy and over a few days he started to act normally again and was even eating a little bit.  

Well, now he's become picky and will not eat his usual food.  So this morning, I went to the store and bought one of every flavor that they had in his food brand.  When we got home my 3 year old chose which food to give him to try out.  He ate half a can of Salmon/Tuna blend and within 5 minutes he got sick.  About an hour or so later he got sick again.  

I'm sure all this thrown together has probably gotten confusing.  But...  I guess my question is, could it be the tuna that is making him sick this time and perhaps his belly is still bothered by it which is why he got sick a second time?

Anyway, if this is confusing, I'm sorry.  I will try to simplify if needed.  

I'm not familiar with Scentsy, but if it contains essential oils, those are known to be problems for cats. Which Scentsy product are you using? If you think Scentsy is the issue, I would definitely discontinue all use to see if that helps. If not, it may be a coincidence, and there's something else going on, either intolerances to food, or some other issue. Generally, thickening of the intestines is a sign of IBD. Did the vet mention why his protein and albumin were low, at least suggest possible causes?

I was so excited to get an essential oil diffuser to use in our home!  Within a few weeks, one of my cats started having these asthma like coughing fits.  When I stopped using the diffuser, her coughing fits greatly diminished.  I would stop using the Scentsy products for 6-12 weeks and see if things change.

If I were you, I would just stop using the scent.  Period.  

Cats can be allergic to fish, as to chicken or beef.  Try offering a chicken based food next.

Some cats are allergic to fish.  My older cat was and every time I fed her any tuna or anything with fish in it, she'd vomit it back up.