Angry father

I love my dad so much and I always do my best to do right and to make him happy and proud but I just never seem to. Everything I do wrong, he points it out. Even the smallest of things. I can't think of any examples because I'm too upset right now. He had asked me to pick up his prescriptions yesterday and I forgot. I know I screwed up but sometimes people just forget things. I said sorry and said I'll get them tomorrow. Today he angrily asked if I got them yet. I said no because my brother was borrowing my car. He said "forget it never mind." I told him I was going into town and I would get them. I did pick them up and and apparently they gave him the wrong one. He had told me he got it switched but he takes so many different kinds that I get them mixed up. They are always changing. So now he's mad at me. He asked what was wrong with me and told me to just go to bed. So now I'm in bed and crying. Every time he does something like this it just makes me not like being around him. I know he's going to have trouble taking the medicine back because I used my debit card and he doesn't have it. I'm afraid for when he realizes that. He gets so angry and hateful. I don't know what to do.