We only dated for 3 weeks but this feels worse than any other breakup. Anybody else been through similar?

I don’t even know if I’m fully heartbroken yet, or if I’m just stuck because I never got any real closure. The relationship ended over WhatsApp, and I never got the chance to talk things through face to face or even on the phone.
A week before we broke up, I pushed back on something because I was feeling insecure. She thought I was breaking up with her. I agreed to talk on the phone, then the next day she said she couldn’t and asked if we could meet instead. We met, talked for hours, and I genuinely thought we’d worked through it.
A couple of days later she ended things by WhatsApp. Her message was kind, thoughtful and honest, and I understand her reasons. But compared with how she’d been before, the change in tone felt so sudden that I’ve been left feeling confused, lost and really hurt.
I also carry a lot of regret because I feel like my insecurity and the way I handled things the week before played a big part in pushing her away.
It’s been nearly two weeks since the breakup, and I haven’t had a proper night’s sleep. Last night and tonight have been the worst. I’m starting to worry about my mental health because I just can’t seem to settle.
Has anyone else experienced something similar after such a short relationship? How long did it take before you started feeling like yourself again? I genuinely feel like I’m losing perspective.