My already grown hair has definitely got stronger and thicker since micro needling.
I'm sorry, but what you just claimed is simply scientifically impossible, I'll explain why. For a hair to get "stronger" or "thicker", it has to be produced like that since the root by the follicle. An already grown or existing hair CANNOT increase its thickness. It has to be shed first, and then replaced by a newly thicker and stronger hair by the follicle. That's why it's highly unlikely to see positive results two weeks apart, no matter how a good responder you are. The only way we can observe progress in such a short time, is by spotting newly growing vellus hairs, but not by feeling already grown hair getting thicker. That may only be imagination, and as @byebyehair said, it's not an objective assertion, but rather a subjective and optimist claim. Optimism is good, and it's good to keep motivation up, but only if we keep a reasonable amount of objectivity and stay on ground.
Does this mean it isn't working? No. It probably is, but it's too early to see results. I believe, however, that needling may improve scalp health overall, so your feeling about a fresher scalp might be objectively true.
Anyway, this by no means should take away motivation. Just keep doing it, it will probably work and you'll get results, just expect it to be really slow, as some long term users have told us.