Hi.
Trust me, I know how you feel. I think you are in the right. It's normal to be anxious about going to the doctor after so long. I would be too. But it'd be good for a check up; especially after what you heard from your sister. Just to be safe. Tell the doctor your concerns and just be open about it. Your dad is in the wrong. I'm sorry but he is. He shouldn't be acting that way at all.
And, on the dentist matter. It's GOOD that you went. It shows proper hygenie. And that you want to take care of yourself. It was so wrong for them to scold you. Sorry that happened.
Go for it. You got this.