Find a kidney specialist who will want to do the following:
1) 24h urine collection+ blood work to calculate creatinine clearance and to check for proteinuria.
2) Ultrasound of the kidneys and Doppler ultrasound to check for Renal Artery Stenosis
Until then, drop the nephrotoxic NSAID and (potentially in those with CKD) creatine. Reduce protein intake. I would keep the ACE inhibitor in there until 1) and 2) have been performed. Unless there is one of the few contraindications, ACE inhibitors or ARBs are recommended medications to delay disease progression in CKD, chiefly through their ability to reduce proteinuria. See https://kidneyfoundation.cachefly.net/professionals/KDOQI/guidelines_bp/guide_11.htm
I would not start using Astragalus until you have been properly diagnosed. You don't want to take any drugs that might mask the underlying issue by boosting eGFR without any corresponding changes in histology.
Yeah...this...OP needs referred to a specialist. The first time my creatinine was elevated I went to a nephrologist and ran more tests than a I ever thought existed plus 24 hour urine collection. In my case everything was fine but if it wasn't I wanted to immediately be working with a specialist.
OP: I assume you are working with your GP, which is fine, but don't feel bad about getting aggressive. I'd demand a specialist referral or at the very least maybe he can run many more tests and see one of his partners who has more experience with kidney issues, even if not a specialist at first?