If I were you, I’d look at the P-shot.
Either find a place that done is cheaply enough or go the route I have and DIY it.
You can buy all the gear for around $100, can give you links if you want, you can then do p-shots that some would charge a lot for cheaply as often as you dare to stick a needle in your dick.
This should give a ton of growth factors.
But don’t do a mere 60ml draw if you DIY it, you can do 120ml of blood a time in the centrifuge, 2 batches a day, make a much larger stronger dose of Platelet Rich Plasma.
I can point you to videos on how to do PRP, videos of it being injected (most say you can barely feel it).
Many claims that with pumping you can gain an inch or 2 rather fast.
I figure your problem is either an awfully tough penis, or a lack of growth factors or both.
Either way this might help.
There is also, just FYI the vitamin D3 study, my current research suggests it might not be overly hazardous to take the megadoses of Vit D3 with K2 & Magnesium, but it must be done with care, and while all 14 participants grew in length, some only modestly.
I am going to try and combine the D3, P-shot with pumping, ADS and more for hopefully accelerated results.
~1997 age 18 I was 4.7" BPEL and somehow grew either because I wasn't done growing and or some PE work to a bit under 6 inches without measuring or noticing progress at the time. Girth has always been about 6 inches but is slowly getting larger 6.2" at widest
Current BPEL after a little work is 6.2" also, Bone pressed stretched flaccid 6.5" Will update with gains.