I have a terrible attitude and I want to change it

I just joined here today. I had just made another post called "Pent up rage at work" if you want to read it. It is somewhat related to this but was getting rather lengthy and thought that this was worthy of it's own post. As the title says, I have a horrible attitude. My first reaction to anything is always something negative or doubtful. I try to think positive, but you know when you are trying to think positive, that is not your real reaction, it is just a reaction to your negative reaction. A battle to the initial thought. And it seems insincere and then overall, my positivity looses. What may be worse is that I know that it comes from my father. He was just like this except worse and it was vocalized. Never anything positive from him. I always heard about it when something was bad like if I didn't make a good grade in school but then when I did, hardly ever a word, maybe a half hearted "good job" but it was more like ok you achieved my expectations rather than I'm excited for you. My mother on the other hand is not like that, however she is somewhat meek and quiet and was not head of the household, and of course me being a male I looked up to my father a lot. And I feel like the battle in my head is just like the situation growing up. My father makes the initial strong negative remark, then my mom counteracts it with a gentle reminder, but it is not enough. And the situation ends up being a disappointment. So now, this dominates my life. Every time I have an idea, it is shot down even if I know it is good. There is just something I can't shake that will ruin things. For example, I may think, hey maybe i'll get into ice climbing, then I'll be like naw, why would I want to do that? There's no point, it's just another way to walk around the earth pointlessly. Then I'll be like, well in that case, what is the point in anything, you are just going to die in the end. Then I will think, well thats just not a good attitude, if you are going to live here, you might as well do it. But something still lingers, something that is not completely satisfying me like to where I would be like yeah, I definately need to go ice climbing. And I can never enjoy anything I do. These thoughts just ruin everything. And I'm just like ok just shut them out, and don't think about it. But really, I feel like they should not exist. Like when I see people that are really into ice climbing, I think, I wonder if they ever think that this is not worth it. And then I figure no, probably not, and they are probably full on enjoying this, and that is why they are because to them, it's absolutely the greatest thing. But to me, there's a problem with it. And I just don't get it. I have a problem with literally everything...and it is ruining my life. For example, I have been committed to going to the gym since the new year. But some days I just wonder, why am I doing this, who cares if I am strong or not, if I look good, if I am in good health, you gotta die sooner or later, and besides that it's kinda narcissistic anyways. And then I'm like well ok what are you going to do, quit? Just go sit on your butt? No you got nothing better to do anyways. And I go along with it, but you see how that kinda ruins it? It's like that for everything. I do things just because I feel I should, like I don't have a choice, but I never really get that feeling that things are worthwhile.