I have the same problem. My mom and dad were always the most affectionate people in the world, to each other. My mother was never the touchy feeley type. My dad we'd give a kiss good night. Mom we would but it still seemed forced. Hell I've always felt like she didn't want all of us, my father did.
Well I'm like my mother. Affection is painfully well painful. It has caused alot of problems between me and my husband. He doesn't understand this because he not this way. He'd be all over me every single second if I let him. Well I try to let him. But I know it's forced.
Then three kids have came along. You know it is super hard but I try and think about it constantly. I don't always do the best I'll be honest. My son will climb up next to me in the rocking chair and I try so hard and be ok with it but then he starts being like his father and rubbing my arm, he's just affectionate like that, and he'll kiss me on the cheek. It's so sweet and he's 8 years old so I know this won't last. It's easier with my daughter for some reason.
But anyways I have a therapist and she always just says go and do it constantly. Make an effort to think about it and go and do it. Basically till I get use to it. Well I've been trying that for about 5 years and I still feel forced and I've gotten a bit better. But just a bit. I'm still trying and that is all I can really do. That is all you can really do. I still think I'm horrid at it but I've improved. I never think I'll be "normal" but what is that anyways.
So basically I'm just raising my hand. I guess just try and go do it like I've been told. Supposedly it gets more natural over time. Maybe it does. I do think I have improved.