Well, you definitely appear to be "between a rock and a hard place [health-wise]!" I'm sorry.
500 milligrams is very little. I ingest well in excess of 100 times that amount every day, and have done so for many, many years. Result to me: Virtually perfect health without the need of doctors or drugs [ever].
I can only encourage you, Boz, to persevere in cleaning out/up your GI tract [at a pace you can "live" with]. I do believe your future health prospects definitely depend upon accomplishing that!
If your vitamin C bottle says it is ascorbic acid, then it is [almost assuredly] the correct vitamin C, i.e. L-ascorbic acid.
I wish you the very best of success, Boz, in resolving your current health issue [and gaining better health in all areas of your body].