Red sores/white patches. Not sure best way to treat [pic included)

It looks like bacterial infection to me. Is he in the quarantine tank now? Is your tank heated and filtered? remove the carbon from filter if you have one (it will remove all medication if you keep it in and your meds won't work). I would suggest to try antibacterial food and/or another cycle of antibiotics and keep him comfortable. Keep water stable and clean + give him some place to hide (something he was familiar with if you moved him to quarantine tank). You may also try to cover the tank with towel to help him rest. Depending on the size of your tank (it looks like he is in a glass bowl right now), you may also want to lower water level so he won't have to swim to hard for air. Keep feeding him and vacuum uneaten food asap, to keep water clean.

Columnaris infection. Try and keep him at about 74F.. lower temps for this disease help slow it down. Some say it doesn't help, many say it does. I'd lower the temp a little, if it was my fish.

Forget the bettafix. It won't help this. Here's some suggestions from Darkmoon17's treatment sticky:

Perform daily 100% water change in small tanks or ¾ water change in larger tanks. Make sure to clean the gravel. Treat with Aq.Salt: add 1 tsp/gal Aquarium Salt 3 times, 12 hours apart so that you end up with 3 times the normal concentration. Do NOT raise the temperature as it thrives in temps over 85*F, however, lowering the temperature does not seem to help fight it. Combine salt treatment with Mardel’s Coppersafe, Maracyn I & II, API Erythromycin, OR API Triple Sulfa, combined with Jungle’s Fungus Eliminator (if possible).

I have to be blunt and say your fish is seriously, seriously ill. Try all of the above, as he may pull through.. but yeah, he is one sick little fishy.