Service connected but 0 percent rating, what to do next?

I have submitted a condition called psoriatic arthritis and it was previously denied after getting the nexus letter thru my private rheumatologist. I went thru the HLR process and the lady on the phone said they didnt consider the nexus letter and they will revise the issue and said I will get on the C&P exam, but I didn't get the exam but rated 0% today.

I have been going to VA for biologics and medications for this condition for the past 6months. Do I need to start gathering medical records and medications and submit it as supplemental claim to see the rating increase? What should be my next step