Check engine light?

So a couple of months ago my Check engine light come on. I took it in and the guy says it's the CAT, so I waited till I had the money since it wasn't something that needed to be fixed right away. And it was running great as usual. I finally replaced the CAT on Monday and he cleared the code and off I went. 20 minutes into the drive the light came back on, so a U-turn I did and took it back. He checked the code and 4 more codes came up. Temp sen: O2 sen: EVAP: and CAT...... soooo he then cleared them again and left for a test drive. He states the light came back on so he re-tested it again. and only 1 code popped up. something completely different. He said that it was probably my computer that needed to be replaced.. Does anyone have any insight to my problem? PLEASE I feel like I'm shooting in the dark here.. Why would it trigger different codes each time. even codes that I have already fixed. Please help. thank you

 

Sorry you had to buy an expensive CAT you really didn't need if I had seen this post before than I would have told you to run SEAFOAM through the input manifold vacuum line and you could have solved that issue with just spending $8 . Lot's of folks these days who are getting cat inefficiency codes are being told to replace the cat when all they have is carbon buildup and 80% of the time it can be cleared with a good cleaning of seafoam.
Yea if you replace the CAT it'll fix the problem but that's going about it the expensive way. Why not give it a good cleaning with seafoam first and see
if that fixes the problem, you won't hurt anything.