I have some real trust issues. Not as much with strangers (even though I do I have a problem there that is more related to a different past trauma). People I generally care about who are close to me tend to be where it really reveals itself. If you're a stranger and you say you'll do something, sure whatever; of course I don't rely on their follow through but it really doesn't stress me out. When they're people I know and say they'll do something, meet me, talk with me or help me in any way; not only do I not believe them, I get this overwhelming feeling like they really don't even care and I'm just a burden to them if they actually do follow through. I actually prefer it when they don't. That stems from whenever my dad would do something for me, like give me two dollars for lunch, and then proceed to make me feel guilty as hell for accepting his help. He'd go into detail how it was such a burden to by food for the week and so on. It's weird because I feel like they'll let me down but I'd rather they do that than actually follow through. Don't know how much sense that actually makes but there you go.
I also have trouble with the appointment thing, too. I just don't make them and it's caused me a lot of problems. I currently need surgery, a PET scan, and a follow up and refuse to make any of them actually happen. Didn't know why but what you described sounds a lot like me and it makes sense, sorry I don't have any advice to help out on that one.