I’d say eftach that you can be experiencing real happiness, yet others can be even happier in at least a particular scenario. Or vice versa. Emotions are not static. The happiness one feels when one makes a $1000 is happiness, but it’s not the same as $10,000 or $100,000. Same with ruchniyus or for example simchas and life events (births).
I feel the root of the issue is not self esteem for you ;-), but the inability to appreciate the moment. Let me say that it is very normal. Any person who has something, will naturally ponder the possibility if they had more of that thing. L’mashal, they go into a delicious restaurant and get a great dish. Meanwhile, they see other great dishes. It’s only natural to wonder if theirs was as great as the others. One learns a blatt, and its great. But they note that there is so much to learn. Maybe they didn’t do what they should have? Maybe they didn’t accomplish or experience what was real learning?
Of course wanting to improve, wanting more good things is not bad. But by and large, a person needs to instill in themselves the greatness of the moment. One when is happy, let’em be happy. Let’em think of great state they are in. Let them thank Hashem for the kindness he has bestowed by doing something to make one happy. To analyze the potential that one’s happiness is insufficient is not not-normal but unhealthy.