The truth is that two months is too short a time to see significant results, especially on your skin. Collagen takes quite a bit longer to notice - we're talking three, four months minimum if it's even going to work at all. For joints it's less painful to wait because there's more scientific evidence that it helps with inflammation, but even then it depends a lot on the dose and whether you're taking it regularly. The thing is: are you drinking enough water? Taking vitamin C? Because collagen doesn't work on its own, it needs everything else together.
I personally took it for a few months because of my joints and I think it helped a bit, but it was no miracle. I noticed more of a difference when I started doing stretches and moving better. On my skin, honestly, I think the most important factor is a good-quality moisturizer, sunscreen every day, and getting good sleep - that makes way more of a difference than any supplement. Why did you start with sagging? Is it age, lifestyle, weight you lost? Because if it's genetic or the result of rapid changes in your skin, powdered collagen might not do much.
If you want to keep going, that's fine, but honestly evaluate it in another two or three months. Compare photos from six months ago to now. And see if there were other changes in your routine during the same period - sometimes we change several things at once and then don't know what actually helped.