I'm gonna use this post as an opportunity to get some conflictions I've felt in my heart out into the world.
After learning that there was such things as "hot" people and "non hot" people I struggled with self image constantly.
The saying "hell is other people" really sticks with me and characterizes alot of how I would grow to view myself. In terms of my body fat, my barrel chest, my facial structure, and my thinning hair, my view point on the way I look could be characterized as unhealthy at best, and profoundly worrying at worst. In a sense, I'd fully internalized this idea that I'm not attractive.
This translates into today quite interestingly. I left my shitty job, moved to a walkable city, got back into school, got a good workout routine, I'm eating much healthier and now in seeing significant results in how my body looks.
I should be happy right? That's the thing, I am happy. It makes me feel really good. I feel desirable and, sometimes, even a bit hot. Not movie star hot but I've noticed when I crack a smile at people I get a blush or an interested response rather than a neutral or just friendly one.
I guess the bulk of why I wanted to write this is because I feel conflicted about how I never overcame this negativity towards myself based on appearance. If I firmly believe others shouldn't be judged for their outward appearances, then why couldn't I ever internalize it, why can't I bring my mind and subconscious understanding to reflect what I've been taught to believe, what I think is right.
I suppose I haven't got a major point to make. Maybe the healthier body has made a healthier brain and that made me hate myself less. However, I think that may be too simple of an explanation. I'm just frustrated with this sense of learning that, to my subconscious anyway, the fucking shit head vapid and vain ideology infected me so much I was incapable of self love until I reached a point where I thought it was okay to do that.
Maybe you guys have some thoughts from reading this? Regardless, I hope you're doing well comrades and I hope you're getting fit and healthy. 
I'm on my phone so I can't really go In-depth, but my read from a very academic, very theory-heavy place, is that there are two separate things here, that we often conflate under the same umbrella because they are dialectically linked, but they work under different mechanisms.
One, is what Foucault would call the "policing of the body": in short, western, capitalist, industrialized society has created all these institutions (like white supremacy, fatphobia, patriarchy, cishet normativity, neutotypicity, etc.) out of a necessity to exert control and have workers "fit into their place", by pressuring on the physicality of the individual, sometimes materially, in the form of violence, but also shaping society's functioning by the pervasive nature of these norms and their enforcement. Body positivity, as far as I know it, stems from a critical view of these systems of policing peoples' bodies and their relationships, checking on those tacit assumptions and asking what purpose they serve in obstructing liberation. You can't shake off the chains you don't know drag you down and so on. I don't have much more modern references for body positivity, so if anyone has a good read, I'd appreciate a recommendation!
So body positivity as a collective goal is a liberatory one, one where people aren't being thrust upon them goals that serve only to undermine their agency. This can take the form of radical body acceptance and activism toward that goal, but it can mean reformulating and questioning the way we relate to ourselves and each other for example by identifying biases in medicine, and correlating body policing to other oppressive structures. The point is that the body should not be a site of oppression for anyone, no matter their shape or ability, and we should fight for that to be the case
On the other hand, (and I swear I'll be brief here) you have mental and physical health, which no matter who you talk to, includes taking care of yourself, especially stemming from a place where you see yourself as a person with the right to dignity and a full life, to the best of your ability (disability is a completely different thing I'm extremely unqualified to talk about). As others have pointed out, you have made changes in your habits, and they seem to have had a positive impact on your mental and physical health, with the added bonus of making you feel better about the way you look. Of course, this last part is informed by the policing structures I spoke about before, but based on the liberatory framework of body positivity, only you, and you alone can gauge what that dignity and happiness looks like. I don't think it's vain to be happy with your choices having desired effects, it's natural, even healthy in my opinion. It's linked to what society expects us to look like and act, and that shapes the way people react to us, but it doesn't invalidate your experiences.
All this to say that it's not wrong to feel good about yourself after you've made changes to improve your situation. You're not a martyr, and no one who cares about you should expect you to be happy in misery and miserable in abundance, that's some weird protestant brainworms. There's societal and psychological baggage that can and should be pushed against, and if you're feeling good about yourself you're going to be a much better part of our collective struggle.