Lost sight of happiness

Hi, I'm new here, guess I'm gonna just put all my thoughts of my life her cause honestly, I don't understand it and maybe you can help me. I feel sad, irritated and anxious most of the day, I feel like it's a task everyday to feel normal. My ex cheated on me three years ago and we broke up, ever since then I think I've been sad.. My home isn't an entirely happy place either. It's been three years and I have achieved so much that I wanted and I feel like i should be grateful and happy for everything I have. But I'm still sad and depressed and I do not know why and I don't know how to be happy? Is it normal to feel this way? My life in general is very hectic with a lot of work and studies. But again my peers don't seem to crib about it as much as I do and I don't assume that to cause my sadness.