How to treat very very old dark spots [Routine Help]

I'm 24 years old, I have sensible skin and dark spots, but I feel like more are appearing even though I've always used sunscreen. 5 years ago I had a pimple on my nose and the dark spot never faded, that happened to other pimples or even blackheads. My blackheads always get dark and bumpy and the spot doesn't fade, because in 4 weeks the blackhead I removed is back, dark and bumpy again.

I use 10% vitamin c in the morning with sunscreen and tinted sunscreen on top of my spots. At night I use 0,05 tretinoin (my skin is too sensitive) and I've seen zero progress, in fact I'm only getting more and more dark spots after each pimple. How do I better my routine? Or are old dark spots forever?