My Dad died when I was just 24. Very suddenly, too. Then my DCs Dad died in 2014.
I miss both of them very much, even though DCs Dad & I were not together then, but I was very close to him and he was very close to our DC & DGC.
It does get easier with time, you really just have to get used to your Dad not being here anymore!
Although, he is obviously still very much with you in spirit, deep in your heart which is exactly where he should be!
I found it eased me a bit to sit somewhere quiet & chat to my Dad, as if he was still there. I'd focus on a part of the room or something within it that I felt was where he might be sitting that day. I felt silly at first, but soon it became easier. Maybe you could try this, too!
My mum would talk to him, oftentimes when she was doing her chores and would say that he'd have had them done in half the time, even with just his one eye! 😆 (He had both eyes but had damaged one and had lost the sight in it).
As my children grew, I'd get them to say good night to Grandad and they'd wave at the stars. In later years, when they knew better, I didn't half get stick for that!! Lol
It doesn't help at this time of year, either. The early dark nights can leave many of us feeling depressed, maybe you could chat with your doctor about your feelings. It's possible they may offer you antidepressants for a little while, to help!
I had my Dad for just a short lifetime, while yours was around much longer, so of course you'll miss him!
Anyone who is close to us/us to them is badly missed when they go. Its human nature.
You're not being silly, and definitely do not let anyone tell you you should be old enough to get over it already, because they obviously haven't grieved for someone so close!!
Do you have any of your Dads clothing, maybe a shirt? If so, and you have a spare dining chair, hang it over the chair at Christmas and bring him to the table, you'll feel his presence then and hopefully be happier for it. Likewise, you could drape something over a comfy seat in front of the TV, and he'll be there watching with you - and don't be afraid to cuddle his clothes now and then if they help you. xx