Hey @Mok and welcome to the forum.
I'm sorry to hear you're experiencing that emptiness. How long have you felt like this?
Something that stood out to me in your post is that "I should be over the moon". I find 'shoulds' are something I feel often and strongly, and they're very hard for me. I think we're taught a lot of shoulds and there are so many of them around events like having a baby and buying a house. While there might be happiness or moments of happiness for some in these events, that's not the case for all of us. They're often big stress and change events and that can be really tricky and extra tricky when we don't feel like we think we should. Is there anyone in your life you are able to talk with about how you're feeling?
Your question of whether anyone has found lasting happiness had me wondering what happiness actually is and how different happiness might be for everyone. For me happiness includes having meaning and purpose. It's having interests and doing things that bring me enjoyment. A big part of happiness for me is found in moments where I feel a sense of peace, calm, curiosity, wonder, stillness, fun, surprise, excitement, appreciation... etc., even if they're fleeting moments. My mental health challenges can make it very hard for me to feel these things. Sometimes I have to work really, really hard to even see them and sometimes I wonder whether they're enough. It can be very tough when I'm sitting in that place where it feels like they're not there. It can help me to try and remember that nothing is forever and to think that even though I can't see them right now, it doesn't mean they are not there. It's so much easier said than done at times though!
I guess the short version of my answer is that I believe happiness exists out there somewhere always, but I can't always see and feel it.
I wonder what happiness means to you (if you feel like sharing)?
Looking forward to hearing what others say about this. I hope you find it helpful to be here.