First of all, my condolences! It must be hard to lose a father at a young age.
Crying at funerals is not mandatory. Never let anyone tell you that you are a horrible person just because you didn’t shed bitter tears!
As @Farah_DeSantis said, everyone deals with grief differently. Some people could lie in bed for weeks and cry. Other people process their grief emotionally and mentally. Some people are looking for logical explanations. And then there are others who are in shock, so they aren’t able to realise the death of their loved one.
Not everyone has to cry to show emotion.
When my great-grandfather died 9 years ago, I didn’t cry at his funeral either, although I was devastated and I was close to him. Some relatives of mine were mad at me because I didn’t weep bitterly. I’m sorry but, that’s not how I mourn. People should start to understand that not everyone has to cry when they grieve.
And I don’t think your father would hold that against you if he could see you. He knows that you love him. Love matters more than tears. 