Întrovert/quiet/shy people problems

Introverts are not necessarily shy or quiet. Being introverted is multi-faceted, and has much more to do with the *way* you socialize, rather than how much you socialize. For example, introverts are more likely to want small groups of people instead of big crowds, to have intimate and quiet settings rather than loud and boisterous, etc etc.
According to what you've said, the label of boring seems to be coming from you, and not the people you are talking to. Crossing ones legs is not a sign of discomfort, generally speaking... Neither is tucking your feet beneath your chair. Yes, body language can be a cue to the feelings of others, but if you are asking outright or stating apologies, and they are saying everything is fine, you should trust them. They aren't lying simply because they choose to say it's fine. In fact, insisting the subject, asking the questions or probing about their personal feelings regarding your social skills could very well be generating the discomfort you perceive.
Once you establish that you're the person to ask those types of questions, people are more likely to have their guard up when spending time with you. Perhaps instead of trying to find their lies or discomfort, you should make the effort to be an engaged listener, and ask questions related to what they are talking about. If they are wanting or asking to spend time with you, then you should take that as an acceptance of your quiet and reserved nature. Ultimately, it is your decision as to how you will handle your feelings and how you will socialize. You can either choose to not socialize with people more extroverted, or you can choose to accept that you are different people and that's okay.

As someone who is also introverted and quiet, there is absolutely nothing wrong with you. I think the reason why people get so uncomfortable around quiet people is because they don't know what your thinking and it becomes hard to read such a person but that doesn't mean there's something wrong with you. There are soooo many people our there with the same personality traits and when they come around people they can relate to, they're surprised to find a totally different them. I think its the same with you and most everyone. But to me, there's nothing wrong with you.

First off, it's not pathetic at all to buy a book that teaches you how to talk to people. You might think that people are either naturally good at conversation or not, but talking is more of a skill. And like all skills, you have to learn it in some way, and you have to practice.

I hate to say it, but you should learn how to hold up your end of a conversation, though. It's not fair, and it's not your fault, but a lot of life revolves around talking to people, and people who are good with people have an easier time.

But that's not to say you should talk all the time. Instead of being quiet, ask the other person questions. You can say "Hello, how is your week going?" when you greet them, you can ask "What's your favorite band?", you can even wonder what they think of the weather- anything to keep a conversation going. Most people, especially extroverts, love talking about themselves, and it takes the pressure off of you. (Asking questions is also a skill, by the way, and after a bit, you learn which things you can ask to get a person talking.)

Of course it's not your faul!
Everybody's different and that's OK. Each of us has the right to talk as much as we feel like talking, and you mustn't feel guilty if you don't feel comfortable when talking.
The truth is that most of the population is extroverted, so it's natural that you are expected to be so as well. But if you are not, you shouldn't be judeged. There's plenty of people who enjoy silence over a conversation, too.
I don't think you are around "the wrong people". However, you should consider meeting some introverted people you can go to when you feel rejected. It's nice to hang out with people that talk like you and about things you are intrested in.
Please bare in mind that the fault is on those who judge, not in those who are just themselves! Good luck~