Is he eating? Still symptomatic?
RI's = vet visit with a qualified reptile vet, and sooner rather than later.
If it's an RI, they will have to do a Tracheal Wash to determine what kind of RI (bacterial of fungal) and what type. Otherwise, you are throwing darts trying to treat.
Our Carpet Python, Yafe, came with an RI because Fedex lost him and his package. An immediate vet visit, tracheal, and proper antibiotic injections and then nebulizer treatments saved his life. He was young and about 100g then. He's now almost 2kg and 7ft and is doing great.
In his case it was stress from travel and low temps. However, stress, humidity too high or low, improper temps, etc. can all cause RI's.
Once you find out what's going on and cure your snake, you will want to figure out why he got it in the first place.
We are here to help. Let us know what the vet says and we can be of more assistance.