How Can i Overcome my issues with showing affection to my girlfriend?

I worked so hard to better my life the past year. Made a ton of friends, lost 30 pounds, and now have a girlfriend that is the first and only person I truly love. But the one problem that I just can't kick is my issues with showing her affection. I want to so bad, things like holding her hand, having my arm around her, kissing, that kind of stuff. We've been together for 3 months and the times I did kick myself in the ass it felt so good. But 99% of the time it's like I just can't. I honestly don't know what's wrong with me. I'll think about finally kissing her beyond just the cheek and I'll get excited but in the end even holding her hand is challenging for me and I have no idea why. I love doing it, she's alright with it, so why am I so closed emotionally? Like I'll go on a walk with her during the break hours of school and think about holding her hand the whole damn time but I just can't do it. I don't want her to feel like I don't love her and I just want to be free of my fears. My problem might stem from the fact that I've been in a pretty ignoring family for a long time but that's just making excuses. Thanks to anyone who read this. I can't think of anyway to improve this problem other than "grow a pair" on my own and I've been trying to do that for so long.