I've been in a similar place with respect to lack of progress and feeling disheartened. Something that helped put some more sweetness into the bittersweet experience of having built a habit but it doesn't feel like it's working, is knowing just how significant exercise is for human health.

My field of study isn't fitness, but being a scientist and also a nerd meant I rabbitholed into the whole fitness thing when I got frustrated with inaccurate or misleading "bro-science". There's a lot we're still learning about how fitness works, but it seems like something that is basically true (as close to a medical consensus as I've ever seen) is that pretty much all humans are healthier with exercise, whether you're fat or thin or fit or unfit. What exercise level is appropriate varies person to person, obviously (people who are overweight may find swimming easier than running for example), but basically everything you're doing is fucking gold. My actual field of research is in biochemistry, so I'm most interested in the remodelling that happens at a cellular level, but I cannot state enough how significant getting up and about is. This kind of progress is even harder to measure or notice than muscle mass or body shape, but know that it is happening, and that your efforts aren't for nought.