Hiya
Sorry to hear you are feeling like this, your post sounds like me a while ago.
It's hard to explain but I didn't feel I deserve to be happy, was having counselling for PND and stumbled upon this. My counsellor asked why and I couldn't answer, I'm not a bad person, I haven't done anything to be punished for, being happy doesn't mean disaster, that I was not chosen by someone at birth to be perpetually unhappy and I shall not enjoy life. But I had a huge issue in my life at 11 when my dad killed himself (DV, cheating etc so should have been happy really) and so I didn't want to get happy again because of the huge crash when it goes wrong or something changes.
But everyone deserves to be happy, we only have one life and I want to live it and not be a bystander, god it was so hard to not look for the pitfalls and worrying about stuff for example when I had organised a childfree day with DH i kept thinking it would fail, I don't deserve to have a nice time but it was great and I had to constantly tell myself to have a good time, to tell myself it was fine to be happy.
And yet another evening my DH and I had planned my DD was taken to hopsital but had to see it was a coincidence, and that's all it was.
Still have good and bad days but the thought that I cannot answer the question why don't I deserve to be happy gets me though.
The feeling when you are happy is amazing, you just need to take a leap of faith and see the setbacks for what they are, a small setback but you are still pushing forward!